Reaction kinetics of PO2Cl-, PO2Cl 2-, POCl2- and POCl3 - with O2 and O3 from 163 to 400 K

Article abstract of DOI:10.1021/jp047545q

Rate constants and product ion branching fractions for the gas-phase reactions of O₂ and O₃ with the anions (a) PO ₂Cl^-, (b) POCl₃^-, (c) POCl ₂^-, and (d) PO₂Cl₂^- were measured in a selected-ion flow tube (SIFT). The kinetics were measured at temperatures of 163-400 K and a He pressure of 0.4 Torr. Only PO ₂Cl^- reacts with O₂ to a measurable extent, having k(163-400 K) = 1.1 × 10^-8(T/K)^-1.0 cm ³ molecule^-1 s^-1, while O³ reacts with all of the anions except PO₂Cl₂^-. The fitted rate constant expressions for the O₃ reaction with anions a-c are as follows: k_a(163-400 K) = 3.5 × 10^-6(T/K) ^-1.6, k_b(163-400 K) = 4.0 × 10 ^-7(T/K)^-1.2, and k_c(163-400 K) = 3.7 × 10^-7(T/K)^-1.4 cm³ molecule^-1 s ^-1. Calculations were performed at the G3 level of theory to obtain optimized geometries, energies, and electron affinities (EAs) of the reactant and product species, as well as to determine the reaction thermochemistry to help understand the experimental results. The PO_xCl_y ^- anions that have lower electron binding energies (eBE) and higher spin multiplicities are more reactive. The doublets are more labile than the singlets. How the extra electron density is distributed in the anion does not predict the observed reactivity of the ion. The reactions of PO ₂Cl^- with O₂ and O₃ yield predominantly PO₃^- and PO₄^-. The reaction of POCl₂^- with O₃ yields mostly Cl^- and PO₂Cl₂^-, while the POCl ₃^- reaction with O₃ yields mostly O ₃^- and PO₂Cl₂^-.

Full text of DOI:10.1021/jp047545q

9120
J. Phys. Chem. A 2004, 108, 9120-9125
-
-
-
-
Reaction Kinetics of PO2Cl , PO2Cl2 , POCl2 , and POCl3 with O2 and O3 from
1
63 to 400 K
†
Abel I. Fernandez, Anthony J. Midey, Thomas M. Miller, and A. A. Viggiano*
Air Force Research Laboratory, Space Vehicles Directorate, 29 Randolph Road,
Hanscom AFB, Massachusetts 01731-3010
ReceiVed: June 7, 2004; In Final Form: August 12, 2004
Rate constants and product ion branching fractions for the gas-phase reactions of O
2
and O
3
with the anions
-
-
-
-
(a) PO Cl , (b) POCl , (c) POCl , and (d) PO Cl were measured in a selected-ion flow tube (SIFT). The
2 3 2 2 2
-
2
kinetics were measured at temperatures of 163-400 K and a He pressure of 0.4 Torr. Only PO Cl reacts
-
8
-1.0
3
-1 -1
with O
2
to a measurable extent, having k(163-400 K) ) 1.1 × 10 (T/K)
cm molecule s , while O
reaction with
3
-
reacts with all of the anions except PO
2
Cl
2
. The fitted rate constant expressions for the O
3
-
6
-1.6
-7
-1.2
anions a-c are as follows: k
a
(163-400 K) ) 3.5 × 10 (T/K) , k
b
(163-400 K) ) 4.0 × 10 (T/K)
,
-
7
-1.4
3
-1 -1
and k
c
(163-400 K) ) 3.7 × 10 (T/K)
cm molecule s . Calculations were performed at the G3 level
of theory to obtain optimized geometries, energies, and electron affinities (EAs) of the reactant and product
species, as well as to determine the reaction thermochemistry to help understand the experimental results.
-
The PO
x
Cl
y
anions that have lower electron binding energies (eBE) and higher spin multiplicities are more
reactive. The doublets are more labile than the singlets. How the extra electron density is distributed in the
-
anion does not predict the observed reactivity of the ion. The reactions of PO
2
Cl with O
2
and O
2
3
yield
-
-
-
-
-, while the
predominantly PO
3
and PO
4
. The reaction of POCl
2
with O
3
yields mostly Cl and PO
2
Cl
-
-
-.
POCl
3
reaction with O yields mostly O
3
3
and PO Cl
2 2
Introduction
of theory to obtain optimized geometries, 0 K total energies,
98 K enthalpies, and electron affinities (EA) are also included
for the relevant reactant and product molecules. These results
have been utilized to determine the reaction thermochemistry
and to help understand the experimental data.
2
The toxicity, reactivity, and decomposition pathways of
phosphorus-containing compounds are particularly interesting
for their role in the use, production, incineration, and accidental
emissions of chemical warfare nerve agents, pesticides, plasti-
cizers, flame retardants, and hydraulic fluids.1-6 Concerns arise
in the contamination of plasma by these compounds in coal-
Experimental Section
The AFRL selected ion flow tube (SIFT)26,27 was used to
make the measurements. The instrument has been discussed in
detail elsewhere and is only briefly described as it pertains to
the current experiments. The ions were formed in a remote
moderate pressure electron impact ion source at about 0.1 to 1
7
fired magnetohydrodynamic electric generators. Also, flame
tests intimate that the addition of a few percent of either
phosphine (PH3) or oxyphosphorus compounds to hydrogen-
fueled scramjet combustors yields a measurable increase of the
flameholding stability and output thrust in the supersonic
expansion because of enhanced H, O, and OH recombination
-
-
-
-
Torr. PO2Cl , PO2Cl2 , POCl2 , and POCl3 were formed from
POCl3 (Aldrich, 99%). The POCl3 was used as obtained from
the manufacturer except for performing several freeze-pump-
thaw steps to remove condensables. Reactant ions were selected
with a quadrupole mass filter and then injected into a fast flow
of helium buffer gas (AGA, 99.997%) in a 1-m long flow tube
using a Venturi inlet, giving a flow tube pressure of 0.4 Torr.
The He buffer gas was passed through a liquid nitrogen cooled
sieve trap in order to remove water vapor before entering the
flow tube. The reactant ions were then thermally equilibrated
and proceeded downstream past an inlet used to introduce the
neutral reactant. Both O2 (Massachusetts Oxygen, 99.999%) and
O3 were used alternately in this study. The ozone was produced
by interfacing an Orec O3V-0 ozonator to the SIFT apparatus
8
-12
kinetics.
Furthermore, evidence suggests that combustion
is sensitive to and can be enhanced by ion-molecule chemis-
13
try. Consequently, the reactions of certain neutral and anionic
phosphorus-containing compounds with common gases have
1
4-18
-
been studied,
in part to elucidate pathways for PO3
production.1
8,19
To address these issues, kinetics measurements for the
-
-
-
-
reactions of PO2Cl , PO2Cl2 , POCl2 , and POCl3 anions with
the oxidants O2 and O3 (ozone) have been made. Ozone is
interesting because it can attach electrons and it is a very strong
oxidant, while reactions with group V compounds producing
species such as PO2 can be chemiluminescent.20-22 Rate
constants and product branching fractions have been measured
from 163 to 400 K for the POxCly ions mentioned above and
these data are compared with previous work on these systems.
1
4
-
as described in detail in a previous work. This technique
yielded a reactant flow of ca. 5% O3 in O2. At the end of the
reaction tube, a portion of the gas was sampled through an
aperture in a blunt nose cone into a second quadrupole, and the
mass-filtered ions were counted using a particle multiplier.
The rate constants were obtained from the pseudo-first-order
attenuation of the reactant ion signal that depends on the reaction
However, a dearth of studies of the ion chemistry of these
systems exists.1
6,23-25
The results of calculations at the G3 level
*
Corresponding author. E-mail: albert.viggiano@hanscom.af.mil.
National Academy of Sciences Postdoctoral Research Fellow.
†
1
0.1021/jp047545q CCC: $27.50 © 2004 American Chemical Society
Published on Web 09/28/2004

Reaction Kinetics of P Compounds with O2 and O3
J. Phys. Chem. A, Vol. 108, No. 42, 2004 9121
a
TABLE 1: G3 Total Energies, Enthalpies, and Electron
TABLE 2: Bond Lengths (in Å) and Angles (in deg) for
Relevant Species Obtained at the G3 Level of Theory,
Where the Superscripts Distinguish the O and Cl Atoms
Affinities (EA), All Units except EA in Hartrees
total
energy
(0 K)
calcd
EAc
(eV)
PO Cl- PO Cl PO Cl PO Cl PO4- PO Cl PO3- Cl O
-
-
enthalpy
(298 K)
parameter
2 2 2 2 2 2 3 2
b
species
EA (eV)
r(P-O)
1.509 1.491
2.270 2.115
1.630 1.477 1.666a 1.470b 1.508
3
-75.02863 1.338 (1.461)d
-75.07778
O( P)
-75.03099
-75.08014
r(P-O
2
)
1.477
1.666 1.620
1.496 1.620
1.987
-
2
O ( P)
3
r(P-O )
1
O2( Σ-g)
3
-150.24490 0.401 (0.451)e
-150.25963
r(P-Cl )
2.010 1.998
-150.24821
-150.26294
1
-
2
r(Cl -O)
1.700
2.134
O2 ( Πgi)
2
r(Cl -O)
1
-225.31437 2.157 (2.1028)f
-225.39357
O3(C2V, A1)
-225.31826
-225.39754
1
1
∠
∠
(O -P-Cl ) 106.28 106.8
98.8
112.7
114.8
108.2
-
2
O3 (C2V, B1)
2
1
(O -P-Cl )
2
-459.98860 3.609 (3.6127)g
-460.12124
1
2
119.8 134.7c 57.7a 126.7 120.0
Cl( P)
-459.99096
-460.12360
∠ (O -P-O ) 125.95 127.5
-
1
2 3
Cl ( S)
∠ (O -P-O )
114.6 61.2 120.0
123.2
106.9
3
4
∠
∠
∠
(O -P-O )
1
+
-920.06777 2.465 (2.38)f
-920.15805
Cl2( Σ g)
-920.07127
-920.16188
1
2
(Cl -P-Cl )
98.3
-
2 +
Cl2 ( Σ u)
1
2
(Cl -O-Cl )
116.3
2
-535.11685 2.321 (2.276)h
-535.20200
1
2 d
ClO( Πi)
-535.12026
-535.20556
dihed(O ,O ) 136.3
102.0 180.0
125.7
147.6
142.7
-
1
1
2
e
f
ClO ( Σ)
dihed(O ,Cl )
dihed(O ,Cl )
dihed(O ,O )
dihed(O ,O )
110.5
127.8
1
1
2
-610.23871 2.245 (2.140)h
-610.32123
ClO2(C2V, B1)
-610.24282
-610.32562
1
3 f
-
1
104.6
64.1
ClO2 (C2V, A1)
1
2 g
1
-995.16208 2.37 (>2.2)i
-995.24808
Cl2O(C2V, A1)
-995.16647
-995.25362
-
2
j
a
-
4
has two double bonds and two single bonds. O atoms labeled
Cl2O (Cs, A′)
PO
1 and 2 are single-bonded while 3 and 4 are double-bonded to P. O
b
2
-491.58890 3.464 (3.42,k
PO2(C2V, A1)
-491.59301
c
l
m
atom 1 is double bonded to P while the other two share a bond. The
3
.7, 3.6)
-
1
45
2
d
PO2 (C2V, A′)
-491.72030
-491.71624
O-P-O angle agrees with the bounded estimate, 130-140°.
P-
1
e
1
f
2
-566.77622 5.155 (4.95)n
-566.95590
Cl is the reference axis. P-O is the reference axis. P-O is the
reference axis. g P-O is the reference axis.
PO3(C2V, B2)
-566.77102
-566.96044
3
-
1
PO3 (D3h, A1)
2
o
PO4(C2V, A2)
-641.884035 -641.878008 5.067
-642.070234 -642.064763
-
1
to POCl2- upon injection into the flow tube was corrected by
PO4 (C2V, A1)
-
2
3.732 (3.8)p
a similar subtraction procedure because POCl2 is also reactive
POCl2(Cs, A′)
-1336.5486
-1336.5429
-1336.6795
3.71
1.50
-
1
-
POCl2 (Cs, A′) -1336.6857
POCl3(C3V, A1) -1796.67736 -1796.67057 1.586 (1.4)p
POCl3 (Cs, A′) -1796.73562 -1796.72744
with O3. Another breakup product is Cl ; however, a back-
1
-
ground subtraction could also be used as Cl is unreactive with
-
2
29
O2 and O3. These observations are consistent with previous
1
PO2Cl(C2V, A1)
PO2Cl (Cs, A′)
-951.710965 -951.705948 2.145
-951.789794 -951.784401
studies of both dissociative and nondissociative electron attach-
-
2
-
-
ment to POCl3, where POCl2 and Cl are the major and minor
2
15,16,25
PO2Cl2(C1, A)
PO2Cl2 (C2V, A1) -1411.93316 -1411.92673
-1411.72046 -1411.71449 5.788
dissociative products, respectively.
In all cases, the product
-
1
branching ratios were renormalized after making background
corrections.
1
PO3Cl(Cs, A)
-1026.81474 -1026.80895 4.399
-1026.97642 -1026.97046
-
2
PO3Cl (Cs, A)
a
30
The Gaussian 2003 program package was used to perform the
Computational Method
b
calculations. The numbers in parentheses are experimental results from
previous work. Calculated EA using the G2 method.
and Lykke.
Gilles et al.
c
47
d
The Gaussian 03W program package30 was used to perform
calculations on the reactant and product species involved using
the G3 theoretical method. The wave function stability of the
Neumark
4
8
e
49
53
f
50
g
51
Travers et al.
Drzaic et al.
The structure of this ion (see Table
Berzinsh et al.
h
52
i
j
Wecker et al.
31
2
) has a long Cl-O bond that indicates a more electrostatic interaction
minimum energy structures from the Hartree-Fock (HF)
optimization step of G3 at the 6-31G(d) level have been verified
for the neutral and ionic species, with the exception of PO4
neutral as discussed later. The G3 0 K energies, 298 K
enthalpies, and EAs are compared with the literature values
whenever possible. These data are given in Table 1 for the
optimized structures that have the parameters listed in Table 2.
The G3 enthalpies at 298 K have also been used to calculate
the heat of reaction at 298 K, ∆Hrxn, for all of the pathways
discussed in the following sections. The average absolute
which may introduce inaccuracies in the Hartree-Fock zero point
energy (ZPE) value since electron correlation is not taken into account.
To correct for this, an MP2 calculation was performed and the ZPE
was found to be 28 meV greater. Thus, a more accurate estimate of
k
54
l
55
m
22
the EA would be lower by this value. Xu et al.
Miller.
Lohr.
n
19 o
Wang and Wang.
EA(PO
4
) was calculated using the G3B3 method
p
(
see text). Mathur et al.23
time and the concentration of the neutral reactant, the latter of
which is varied during a measurement. The rate constants have
relative uncertainties of (15% and absolute uncertainties of
-
1 31
deviation in the G3 results is (0.041 eV (0.94 kcal mol ).
(
25%.26 For the product distributions, the SIFT was operated
3
2
Additionally, a natural population analysis (NPA) was used
to ascertain the location of the “extra” electron density in the
anions; geometries were optimized using MP2(Full) at the
under conditions of modest attenuation of the reactant ion signal
and the product branching fractions were extrapolated to a
condition of zero neutral reactant concentration. Thus, the effects
of secondary chemistry are accounted for. The mass resolution
of the downstream mass filter has also been adjusted to minimize
mass discrimination during the branching fraction measurements.
The branching fractions have relative uncertainties of (10%
of the major product peaks.28
Because of the unavoidable presence of O2 during the O3
experiments, corrections to the branching fractions for the
PO2Cl reaction with O3 were made by subtracting the product
counts from the O2 reaction with PO2Cl . When the POCl3
O3 system was studied, the breakup of roughly 5% of POCl3
6
-311+G(d) level.
Experimental Results
Rate constants and branching fractions for the reactions of
-
-
-
-
PO2Cl , PO2Cl2 , POCl2 , and POCl3 with O2 and O3 were
measured from 163 to 400 K at a He pressure of 0.4 Torr. Only
-
-
PO2Cl reacts with O2 to a measurable extent, while PO2Cl2
-
was found to be unreactive with both O2 and O3. This
-
-
-
+
observation is in agreement with earlier work where PO2Cl2 ,
-
-
-
17,25
POCl2 , and POCl3 were found to be unreactive with O2.

9122 J. Phys. Chem. A, Vol. 108, No. 42, 2004
Fernandez et al.
a
TABLE 3: Rate Constants and Ion Product Branching
-
-
-
Fractions for the Reactions of PO
2
Cl , PO
2
Cl
2
, POCl
2
,
-
b
and POCl
3
2 3
with O and O
reaction
163 K
294 K
400 K
PO2Cl- + O2
0.60 [6.0] 0.33 [6.0] 0.24[6.0]
-
f
PO3 + ClO
0.49
0.51
0.42
0.58
0.41
0.59
-
PO4 + Cl
PO2Cl- + O3
11 [9.9]
0.62
5.0 [8.9] 2.6 [8.6]
-
f
PO3 + ClO2
0.65
0.66
-
PO3 + Cl + O2
-
PO4 + ClO
0.34
0.04
0.34
0.01
0.33
0.01
-
Cl + PO3 + O2
POCl2- + O3
3.3 [9.7]
0.71
1.1 [8.6] 1.0 [8.3]
-
f
Cl + PO2Cl + O2
0.79
0.60
-
Cl + PO3 + ClO
-
3
-1
-
PO2Cl2 + O2
0.26
0.02
0.20
0.01
0.35
0.03
Figure 1. Rate constants in cm s for the reactions of PO
2
Cl ,
- -
2 3 2 3
POCl , and POCl with O and O as a function of temperature in K
-
PO3 + ClO + Cl
-
PO3 + Cl2O
as measured in a selected ion flow tube (SIFT).
-
PO4 + Cl2
0.01
e0.005
0.02
POCl3- + O3
10 [9.3]
0.50
0.44
4.0 [8.3] 3.6 [8.1]
Moreover, this lack of reactivity is not surprising as the EA of
O2 is smaller than that of POCl3 (see Table 1). The SIFT
apparatus is capable of accurate measurement of rate constants
f
O3- + POCl3
0.55
0.42
0.55
0.44
-
PO2Cl2 + ClO2
-
PO2Cl2 + Cl + O2
-
Cl + PO2Cl2 + O2
0.06
0.03
0.01
-
12
3 -1
approximately as low as 5 × 10 cm s . Consequently, the
-
Cl + PO2 + Cl2 + O2
-
-
-
rate constants for the reactions of PO2Cl2 , POCl2 , and POCl3
with O2 have a value <5 × 10
Cl- + PO Cl + ClO
3
-
12
3
-1
cm s . A similar upper
a
Rate constants in units of 10-10 cm3 s-1; bracketed numbers
limit can be placed on the rate constant for the reaction of
PO2Cl2 with O3 as it is unreactive as well, since no products
represent calculated collisional rate constants obtained by the param-
etrized trajectory approach of Su and Chesnavich.
-
56,57 b
Measurements
-
-
-
are formed.
2 2 2
of the rate constants of PO Cl , POCl2 , and POCl3 with O and of
-
-
-12
3
-1
The rate constants for the reaction of PO2Cl with O2 given
2
PO Cl
2
with O
3
yielded upper limits of 5 × 10 cm s
.
by eq 1
are also shown in Figure 1, while the product branching fractions
are listed in Table 3. A best fit to the rate constants gives the
2
-
3
1
-
2
PO Cl + O f PO + ClO ∆H ) -1.18 eV (1a)
2
2
3
rxn
-6
-1.6
3
-1
expression k(163-400 K) ) 3.5 × 10 (T/K)
cm molecule
1
PO4- + Cl ∆H ) -0.48 eV (1b)
2
-1
s
for reaction 2. Clearly, O3 reacts about an order of magnitude
rxn
faster than O2. The same decrease with increasing temperature
is also seen with ozone. Unlike the previous reaction, the major
are shown in Figure 1. The superscripts in eq 1 and all
subsequent reaction equations denote the spin multiplicity and
only the spin-allowed, exothermic channels are given. The
energetics of the reactants and products calculated using G3
theory for all the listed reactions are also shown in Table 1.
For purposes of efficiency, the rate constant data for all of the
reactions studied are shown in Figure 1. A best fit to the rate
constants for reaction 1 in Figure 1 yields the expression k(163-
-
product ion is PO and its fraction is about twice as great than
3
-
-
that of PO . Also, a small amount of Cl is produced; however,
4
it is less than 5% of the total products and it also decreases
with increasing temperature.
The rate constants for the reaction of POCl2- with O3 given
by eq 3
-
8
-1.0
3
-1 -1
4
00 K) ) 1.1 × 10 (T/K)
cm molecule s . This case
1
POCl2- + O f Cl + PO Cl + O (a ∆ )
1
1
-
1
1
1
is the only one where oxygen reacts to a measurable extent with
3
2
2
g
-
POxCly in the SIFT. Clearly, the rate constants decrease with
∆Hrxn ) -1.15 eV (3a)
increasing temperature, indicative of a reaction involving either
an intermediate collision complex or transfer of an electron.
1
-
2
2
Cl + PO + ClO ∆H ) -0.557 eV (3b)
3
rxn
-
The product ion branching fractions for the products PO3
1
-
1
1
33
-
-
PO Cl + O (a ∆ ) ∆H ) -3.86 eV (3c)
2 2 2 g rxn
and PO4 are listed in Table 3. The fraction of PO4 is
-
somewhat greater than that of PO3 at all temperatures and
1
PO3- + ClO + Cl ∆H ) -1.84 eV (3d)
2
2
rxn
increases with increasing temperature.
The rate constants for the reaction of PO2Cl with O3 given
-
1
PO3- + Cl O ∆H ) -3.34 eV (3e)
1
2
rxn
in eq 2
1
PO4- + Cl ∆Hrxn ) -3.60 eV (3f)
1
2
-
1
1
-
3
2
2
PO Cl + O f PO + ClO2 ∆Hrxn ) -2.61 eV (2a)
2
3
1
PO3- + Cl + O ∆Hrxn ) -2.47 eV (2b)
2
3
are well fitted by the expression k(163-400 K)
)
2
-7
-1.4
3
-1 -1
3
.7 × 10 (T/K)
cm molecule
s
and are somewhat less
1
1
PO3- + Cl + O (a ∆ ) ∆H ) -1.49 eV (2c)
2
1
1
-
than the rate constants for the PO2Cl reaction. Nevertheless,
the rate constants demonstrate the same negative trend with
increasing temperature. The product ion branching fractions in
2
g
rxn
1
PO4- + ClO ∆H ) -2.08 eV (2d)
2
rxn
-
Table 3 show that Cl is by far the major product, while the
1
-
2
3
-
Cl + PO + O ∆Hrxn ) -1.19 eV (2e)
PO2Cl2 yield is roughly 25% and increases to 35% at 400 K
3
2
-
-
-
at the expense of Cl . Trace amounts of PO3 and PO4 were
also observed.
-
2
1
1
Cl + PO + O (a ∆ ) ∆H ) -0.21 eV (2f)
3
2
g
rxn

Reaction Kinetics of P Compounds with O2 and O3
J. Phys. Chem. A, Vol. 108, No. 42, 2004 9123
TABLE 4: Natural Population Analysis of the PO
x
Cl
y
O. Interestingly, most of the extra electron density from adding
an electron to form the anion resides on the Cl atom(s), whereas
the O atom(s) receive a much smaller portion. This was also
observed in the NPA calculation from the electron attachment
study involving POCl3 and PCl3. The behavior of PO2Cl2 is
different than that of the other anions in that the O atoms are
not equivalent and do get a considerable portion of the extra
density. Moreover, the P atom of PO2Cl2 loses electron density
upon attachment.
Speciesa
charge associated with each atom
O1
O2
Cl1
Cl2
Cl3
P
1
6
-
POCl3
POCl3
1.547 -0.95
1.399 -1.012
-0.199 -0.199 -0.199
-0.404 -0.492 -0.492
-
-
extra e
0.15
0.06
0.21
0.29
0.29
POCl2
1.405 -0.929
1.117 -1.022
-0.238 -0.238
-0.547 -0.547
-
POCl2
-
extra e
0.29
0.09
0.31
0.31
PO2Cl2b
1.777 -0.435 -0.944 -0.199 -0.199
1.952 -1.063 -1.063 -0.413 -0.413
Discussion
-
PO2Cl2
-
extra e
-0.175
0.628
0.119
0.214
0.214
It is clear that ozone is more reactive than oxygen, despite
the fact that ground-state ozone has a singlet multiplicity while
ground-state oxygen is a triplet. These results are consistent with
the strong oxidizing ability of ozone. The negative temperature
of the rate constants indicates that either a collision complex
or a transfer of electrons is involved in the reactions. Ozone
PO2Cl
1.980 -0.883 -0.883 -0.214
1.630 -1.048 -1.048 -0.533
-
PO2Cl
-
extra e
0.350
0.165
0.165
0.319
35
a
Superscripts used to label different O and Cl atoms. b Here, the
charges on the two O atoms are not equivalent since the P-O bond
lengths are not equal; see Table 2.
reactions with olefins can proceed via channels utilizing five-
Finally, the reaction of POCl3- with O3 given by eq 4
35,36
membered-ring ozonide intermediates.
If a similar mecha-
nism is involved in these reactions, the ozone could add to the
double bond connecting P and O.
2
POCl - + O f O + POCl3 ∆Hrxn ) -0.61 eV (4a)
1
2
-
1
3
3
3
Alternatively, a four-membered collision complex may be
formed by an O3 attack on the electropositive P atom of the
1
PO Cl2- + ClO2 ∆Hrxn ) -3.36 eV (4b)
2
2
-
37
POxCly ; the approach would be end-on since the terminal O
atoms of O3 are more negatively charged than the middle atom.
The NPA results in Table 4 confirm that the P atom is more
positively charged. The more positive middle O atom of O3
would be attracted to the more negatively charged Cl atoms in
the collision complex. The spin-allowed, exothermic product
channels are listed in Table 3 and reactions 1-4 may well
1
PO Cl2- + Cl + O ∆Hrxn ) -3.22 eV (4c)
2
3
2
2
1
1
-
2
1
1
PO Cl + Cl + O (a ∆ ) ∆H ) -2.24 eV (4d)
2
2
2
g
rxn
1
-
2
3
Cl + PO Cl + O ∆Hrxn ) -1.06 eV (4e)
2
2
2
-
2
1
1
Cl + PO Cl + O (a ∆ ) ∆H ) -0.08 eV (4f)
2
2
2
g
rxn
1
produce ClmOn neutral fragments or O2 (a ∆), indicating that
1
-
1
2
rearrangements could subsequently occur during the reaction
that would result in the observed product ions. A similar
mechanism occurs in the reaction of alkyl cations with O3.29 In
those systems, the intermediate complex forms with the terminal
O of O3 bonded to the positively charged C atom of the ion,
followed by rapid O2 ejection and subsequent rearrangements
to give the final products. HF geometry optimizations at the
Cl + PO Cl + ClO ∆H ) -0.14 eV (4g)
3
rxn
-
is as rapid as that of PO2Cl with O3. The best fit expression to
-
7
-1.2
3
the rate constants is k(163-400 K) ) 4.0 × 10 (T/K)
cm
-1
-1
-
molecule
s
for reaction 4. O3 is the major product, resulting
-
from direct electron transfer, while the PO2Cl2 product yield
is somewhat less. Another similarity with the PO2Cl reaction
is the presence of trace amounts of Cl product ions which also
decrease with increasing temperature.
-
-
-
6-31G(d) level for POxCly‚O3 complexes show that stable
structures can be found having either the ozonide-type or the
-
-
alkyl cation-O3 type structure for PO2Cl , POCl2 , and
-
Computational Results
POCl . More detailed calculations of the O reaction potential
3
3
energy surface and detailed reaction paths for the various
reactant ions are beyond the scope of this work.
Table 1 shows the G3 calculated 0 K energies, 298 K
enthalpies, and EAs of the relevant species. The calculated EAs
and the available experimental values from earlier work are in
excellent agreement. The G3(B3LYP) method was used to
calculate EA(PO4) because of a problem in maintaining the
lowest-energy wave function throughout the HF and Møller-
Plesset (MP) steps of an attempted G3 calculation for neutral
PO4. However, the G3(B3LYP) method is of comparable
accuracy to the G3 method.34
Inspection of Table 4 reveals that there is no correlation
between the electron density on the constituent atoms of the
-
POxCly anions and the reactivity. This observation is similar
to the computational results of Langeland and Werstiuk regard-
ing the reactivity of several neutral tertiary phosphite esters with
O3. In that work using density functional theory (DFT) and
atoms-in-molecules (AIM) methods, no correlation was found
between the size of the activation barriers to produce phosphates
Table 2 contains the optimized geometries of some of the
reactant and product anions. Examining the data in Table 2
shows that the POxCly- anions studied in the SIFT all have
1
and O2 and the atomic charges on the phosphorus atom or
oxygen atoms that make up the four-membered ring of the
-
-
37
nonplanar minimum energy structures. PO2Cl and POCl2 both
phosphite ozonide intermediate.
-
It is interesting to note that only the reaction of POCl3- with
O3 undergoes charge transfer. Of the four reactants, only POCl3
have umbrella shaped geometries, while POCl3 and PO3Cl are
-
tetrahedral. Adding the electron to the PO2Cl neutral shown in
Table 2 causes the trigonal planar structure to distort to the
has an electron binding energy (eBE) that is considerably less
-
-
umbrella shape. The PO2Cl2 ion has the two O atoms on the
than the EA of O3 (see Table 1). The eBE of PO2Cl is about
same side of the P atom arranged trans to the two Cl atoms on
the opposite side.
The results of the NPA computations given in Table 4 show
that the electron densities of both the neutral and charged species
are concentrated around the more electronegative atoms, Cl and
equal to that of O3, and the charge-transfer reaction is thermo-
neutral but is not observed. Not surprisingly, the more reactive
-
-
ions, PO2Cl and POCl3 , have lower eBEs than the less labile
-
-
POCl2 . The unreactive PO2Cl2 ion has the highest eBE. A
-
38
similar observation was made for the SOxFy species. In

9124 J. Phys. Chem. A, Vol. 108, No. 42, 2004
Fernandez et al.
addition, the reactivity can be explained by observing the spin
multiplicities of the anion reactants as shown in Table 1 and
eqs 1-4. The more reactive ions are doublets, and the less labile
species are singlets. Even though examples of fast ion-molecule
Chemistry Laboratory at AFRL under Grant No. 2303EP4. The
authors also thank John Williamson and Paul Mundis for
technical assistance. T.M.M. and A.J.M. are under contract (No.
F19628-99-C-0069) to Visidyne, Inc., Burlington, MA.
3
9-42
reactions that do not conserve spin have been observed;
it
is apparent that both the bond strength and spin multiplicity
can affect reactivity. Comparable effects of spin multiplicity
References and Notes
-
on reactivity were also observed in an earlier study of SOxFy
(1) Corbridge, D. E. C. Phosphorus An Outline of its Chemistry,
Biochemistry, and Technology, 3rd ed.; Elsevier: Amsterdam, 1980; Vol.
43
reactions with O3, where another common feature of the
6.
-
-
SOxFy and POxCly anions is their lack of reactivity with O2.
Finally, as noted above, there seems to be no correlation between
reactivity of the anions and the charges on the constituent atoms.
(2) The Pesticide Manual; 13th ed.; Tomlin, C., Ed.; British Crop
Protection Council: Alton Hampshire, U.K., 2003.
(3) Handbook of Plasticizers, 1st ed.; Wypych, G., Ed.; Chem Tec:
Toronto, Canada, 2004.
(
4) Price, D.; Pyrah, K.; Hull, T. R.; Milnes, G. J.; Ebdon, J. R.; Hunt,
B. J.; Joseph, P. Polym. Degrad. Stab. 2002, 77, 227.
5) Handbook of Hydraulic Fluid Power Technology; Totten, G. E.,
Ed.; Marcel Dekker: New York, 2000.
(6) Korobeinichev, O. P.; Ilyin, S. B.; Bolshova, T. A.; Shvartsberg,
V. M.; Chernov, A. A. Combust. Flame 2000, 121, 593.
Conclusions
(
Rate constants and product branching fractions for the gas-
-
-
phase reactions of O2 and O3 with the anions PO2Cl , POCl3 ,
-
-
POCl2 , and PO2Cl2 were measured from 163 to 400 K at 0.4
(7) Wormhoudt, J. C.; Kolb, C. E. Mass Spectrometric Determination
-
Torr in a SIFT. Only PO2Cl reacts with O2 to a measurable
extent, while O3 reacts with all of the ions except PO2Cl2 .
of Negative and Positive Ion Concentrations in Coal-Fired MHD Plasmas.
In Proceedings of the 10th Materials Research Symposium, Characterization
of High-Temperature Vapors and Gases; Gaithersburg, MD, 1979; U.S.
Government Printing Office: Washington, DC, 1979.
-
Stronger reactivity is favored by the following: (a) the weaker
bond strength of O3 relative to O2, (b) the decreasing eBE of
the more reactive anions, and (c) the higher spin-multiplicity
of the more reactive anions; i.e., doublets react faster than the
singlet species. There is no correlation between reactivity of
the anions and electron density of the individual atoms. The
(
8) Pellett, G. L. NASA Tech. Rep. 1996 1996, 1.
(9) Singh, D. J.; Carpenter, M. H.; Drummond, J. P. J. Propul. Power
1997, 13, 574.
(
(
(
10) Twarowski, A. Combust. Flame 1993, 94, 91.
11) Twarowski, A. Combust. Flame 1995, 102, 55.
12) Mackie, J. C.; Bacskay, G. B.; Haworth, N. L. J. Phys. Chem. A
-
-
reactions of PO2Cl with O2 and O3 yield primarily PO3 and
2002, 106, 10825.
-
-
-
PO4 . The reaction of O3 with POCl2 yields mostly Cl and
PO2Cl2 , while the POCl3 reaction with O3 yields mostly O3
(13) Williams, S.; Midey, A. J.; Arnold, S. T.; Miller, T. M.; Bench, P.
M.; Dressler, R. A.; Chiu, Y.-H.; Levandier, D. J.; Viggiano, A. A.; Morris,
R. A.; Berman, M. R.; Maurice, L. Q.; Carter, C. D. Progress on the
investigation of the effects of ionization on hydrocarbon/air combustion
chemistry: kinetics and thermodynamics of C6-C10 hydrocarbon ions.
Presented at the AIAA 4th Weakly Ionized Gases Workshop, Anaheim,
CA, 2001.
-
-
-
-
and PO2Cl2 . G3 calculations were performed to obtain
optimized structures, energies, and electron affinities for the
reactant and product species and to calculate the thermochem-
istry for the observed reaction channels. NPA calculations show
that the extra electron density added when forming POxCly-
anions is distributed primarily on the Cl atom(s).
(14) Williams, S.; Campos, M. F.; Midey, A. J.; Arnold, S. T.; Morris,
R. A.; Viggiano, A. A. J. Phys. Chem. A 2002, 106, 997.
(15) Knighton, W. B.; Miller, T. M.; Grimsrud, E. P.; Viggiano, A. A.
J. Chem. Phys. 2004, 120, 211.
The results presented above could have implications for the
technologies mentioned in the Introduction. The metaphosphate
(16) Miller, T. M.; Seeley, J. V.; Knighton, W. B.; Meads, R. F.;
Viggiano, A. A.; Morris, R. A.; Van Doren, J. M.; Gu, J.; Schaefer, H. F.,
III. J. Chem. Phys. 1998, 109, 578.
-
anion, PO3 , is interesting because it is very stable and it has
been detected in combustion environments44 while the neutral
(17) Morris, R. A.; Viggiano, A. A. Int. J. Mass Spectrom. Ion Proc.
1
997, 164, 35.
18) Morris, R. A.; Viggiano, A. A. J. Chem. Phys. 1998, 109, 4126.
(19) Wang, X.-B.; Wang, L.-S. Chem. Phys. Lett. 1999, 313, 179.
PO3 radical is associated with phosphorus impurities in coal-
(
fired, magnetohydrodynamic electric generators.7
,19,44
Impurity
(
(
(
(
20) Toby, S. Chem. ReV. 1984, 84, 277.
ions tend to decrease the efficiency of power generation by
dilution of the plasma and by radiative loss. The present work
21) Kampf, R. P.; Parson, J. M. J. Chem. Phys. 1998, 108, 7595.
22) Lohr, L. L. J. Phys. Chem. 1984, 88, 5569.
-
shows that the reaction of PO2Cl with O2 and O3 yield
23) Mathur, B. P.; Rothe, E. W.; Tang, S. Y.; Reck, G. P. J. Chem.
-
significant amounts of PO3 . However, the ozone is more than
Phys. 1976, 65, 565.
24) Goodings, J. M.; Hassanali, C. S. Int. J. Mass Spectrom. Ion Proc.
990, 101, 337.
25) Williamson, D. H.; Mayhew, C. A.; Knighton, W. B.; Grimsrud,
(
an order of magnitude more reactive over the 163-400 K range.
This kinetic information may be of use in the modeling of
impurity formation in plasmas. PO2Cl, for example, has a
1
(
E. P. J. Chem. Phys. 2000, 113, 11035.
modest EA and can be formed by the reaction of neutral POCl,
(26) Viggiano, A. A.; Morris, R. A.; Dale, F.; Paulson, J. F.; Giles, K.;
Smith, D.; Su, T. J. Chem. Phys. 1990, 93, 1149.
POCl3, and PCl3 with O2.45
(
27) Viggiano, A. A.; Morris, R. A. J. Phys. Chem. 1996, 100, 19227.
The PO2 moiety is thought to be a catalyst in the recombina-
tion of H, O, and OH flame species, which can lead to an
(28) Arnold, S. T.; Williams, S.; Dotan, I.; Midey, A. J.; Morris, R. A.;
Viggiano, A. A. J. Phys. Chem. A 1999, 103, 8421.
29) Williams, S.; Knighton, W. B.; Midey, A. J.; Viggiano, A. A.; Irle,
S.; Morikuma, K. J. Phys. Chem. A 2004, 108, 1980.
30) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
(
enhancement of thrust in the supersonic expansion in scramjet
exhausts.8
-12
Apparently, the present reactions studied are not
(
capable of directly producing PO2, as no energetically allowed
channels exist. However, reaction 4 has a spin-allowed channel
that gives PO2, but it is endothermic by about 0.5 eV.
It is possible that reactions 1-4 produce the neutral species
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K.
N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.;
Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.;
Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.;
Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels,
A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson,
Cl and ClO, which are known to participate in the catalytic
destruction of stratospheric ozone.46 This potentially negative
environmental impact is important when considering the use
of oxyphosphorus additives for use in combustion systems.
Acknowledgment. The authors thank the Air Force Office
of Scientific Research for its continued support of the Plasma

Reaction Kinetics of P Compounds with O2 and O3
J. Phys. Chem. A, Vol. 108, No. 42, 2004 9125
B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03,
revision B.02. Gaussian, Inc.: Pittsburgh, PA, 2003.
(43) Viggiano, A. A.; Arnold, S. T.; Williams, S.; Miller, T. M. Plasma
Chem. Plasma Proc. 2002, 22, 285.
(
31) Curtiss, L. A.; Redfern, P. C.; Raghavachari, K.; Rassolov, V.;
Pople, J. A. J. Chem. Phys. 1998, 109, 7764.
32) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985,
3, 735.
33) Huber, K. P.; Herzberg, G. Molecular Spectra and Molecular
(44) Henchman, M.; Viggiano, A. A.; Paulson, J. F.; Freedman, A.;
Wormhoudt, J. J. Am. Chem. Soc. 1985, 107, 1453.
(45) Ahlrichs, R.; Ehrhardt, C.; Lakenbrink, M.; Schunck, S.; Schnokel,
H. J. Am. Chem. Soc. 1986, 108, 3596.
(46) Molina, M.; Rowland, F. S. Nature (London) 1974, 249, 810.
(47) Miller, T. M.; Viggiano, A. A.; Morris, R. A.; Miller, A. E. S. J.
Chem. Phys. 1999, 111, 3309.
(
8
(
Structure. IV. Constants of Diatomic Molecules; Van Nostrand Reinhold:
New York, 1979.
(
34) Baboul, A. G.; Curtiss, L. A.; Redfern, P. C.; Raghavachari, K. J.
Chem. Phys. 1999, 110, 7650.
35) Horvath, M.; Bilitzky, L.; Huttner, J. Ozone; Elsevier: Amsterdam,
985.
36) Gillies, J. Z.; Gillies, C. W.; Suenram, R. D.; Lovas, F. J. J. Am.
Chem. Soc. 1988, 110, 7991.
37) Langeland, J. L.; Werstiuk, N. H. Can. J. Chem. 2003, 81,
25.
(48) Neumark, D. M.; Lykke, K. R. Phys. ReV. A 1985, 32, 1890.
(49) Travers, M. J.; Cowles, D. C.; Ellison, G. B. Chem. Phys. Lett.
1989, 164, 449.
(50) Drzaic, P. S.; Marks, J.; Brauman, J. I. Electron photodetachment
from gas-phase molecular anions. In Gas-Phase Ion Chemistry: Ions and
Light; Bowers, M. T., Ed.; Academic: New York, 1984; Vol. 3; p 168.
(51) Berzinsh, U.; Gustafsson, M.; Hanstorp, D.; Klinkmueller, A. E.;
Ljungblad, U.; Maartensson-Pendrill, A.-M. Phys. ReV. A 1995, 51, 231.
(52) Gilles, M. K.; Polak, M. L.; Lineberger, W. C. J. Chem. Phys. 1992,
96, 8012.
(
1
(
(
5
(38) Arnold, S. T.; Miller, T. M.; Viggiano, A. A. J. Phys. Chem. A
2
002, 106, 9900.
(
39) Fehsenfeld, F. C.; Ferguson, E. E.; Schmeltekopf, A. L. J. Chem.
Phys. 1966, 44, 3022.
40) Paulson, J. F.; Mosher, R. L.; Dale, F. J. Chem. Phys. 1966, 44,
025.
(53) Wecker, D.; Christodoulides, A. A.; Schindler, R. N. Int. J. Mass
Spectrom. Ion Phys. 1981, 38, 391.
(54) Xu, C.; de Beer, E.; Neumark, D. M. J. Chem. Phys. 1996, 104,
2749.
(
3
(
(
41) Ferguson, E. E. Chem. Phys. Lett. 1983, 99, 89.
42) Federer, W.; Villinger, H.; Lindinger, W.; Ferguson, E. E. Chem.
(55) Miller, W. J. J. Chem. Phys. 1978, 69, 3709.
(56) Su, T.; Chesnavich, W. J. J. Chem. Phys. 1982, 76, 5183.
(57) Su, T. J. Chem. Phys. 1988, 89, 5355.
Phys. Lett. 1986, 123, 12.