Steric effects in chemiluminescent reactions of metastable Ca*, Sr* atoms with isomeric propyl halides

Article abstract of DOI:10.1016/S0009-2614(99)00676-4

Reactions of metastable alkaline earth atoms with normal and branched propyl halides were studied in a beam-gas arrangement. Chemiluminescence spectra of alkaline earth monohalides were observed for calcium and strontium reactions. Some differences in the CaX (B ²Σ⁺ / A ²Π) branching ratio were found with isomeric variation of the targets. Total collision cross-sections for Mg^* and Ca^* reactions are independent of the isomeric substitution; for strontium the values for isopropyl iodide are 50% higher than those for normal propyl iodide target. Differences in chemiluminescence cross-sections are found for reactions of calcium with propyl iodides and propyl chlorides.

Full text of DOI:10.1016/S0009-2614(99)00676-4

13 August 1999
Ž
.
Chemical Physics Letters 309 1999 183–190
www.elsevier.nlrlocatercplett
Steric effects in chemiluminescent reactions of metastable Ca),
Sr) atoms with isomeric propyl halides
)
B. Pranszke, P. Kierzkowski, A. Kowalski
Institute of Experimental Physics, UniÕersity of Gdansk, ul. Wita Stwosza 57, PL-80-952 Gdansk, Poland
´
´
Received 29 January 1999; in final form 16 June 1999
Abstract
Reactions of metastable alkaline earth atoms with normal and branched propyl halides were studied in a beam-gas
arrangement. Chemiluminescence spectra of alkaline earth monohalides were observed for calcium and strontium reactions.
2
2
q
Ž
.
Some differences in the CaX B S r A P branching ratio were found with isomeric variation of the targets. Total
collision cross-sections for Mg) and Ca) reactions are independent of the isomeric substitution; for strontium the values for
isopropyl iodide are 50% higher than those for normal propyl iodide target. Differences in chemiluminescence cross-sections
are found for reactions of calcium with propyl iodides and propyl chlorides. q 1999 Elsevier Science B.V. All rights
reserved.
w
x
Ž1
.
1. Introduction
classic ‘rebound’ mechanism 10 . Ba S0 qn-
w x
C3H7 I, i-C3H7 I reactions 4 , on the other hand,
Of the gas-phase reactions between metal atoms
and propyl halide molecules, the best studied are
these involving propyl iodide. There are several pa-
pers on reactions of this compound with various
ground state atoms 1–9 . The studies indicate that in
this case collision dynamics depends mainly on the
identity of the atomic partner. Reactive collisions of
alkali atoms with propyl iodides were found to be
characterized by dominantly backward scattering of
the diatomic products and rather low reactive cross-
appear to be initiated by an electron jump process.
The alkaline earth atom–propyl halide systems have
w x
been little studied in the past. Besides Ref. 4 , there
is one report on the Ca 3PJ , D2 qn-C3H7 I reac-
1
) Ž
.
w
x
tion studied by the method of chemiluminescence
w
x
Ž1
.
11 and a publication on the Sr S0 qn-C3H7 Br, i-
C3H7 Br reactions studied by laser-induced fluores-
w
x
cence 12 .
w x
4 is the only one which addresses the
problem of steric effects in reactions of alkaline
earth atoms with isomeric propyl halides. The reac-
tions of ground state barium with isomeric propyl
iodides were studied there using the method of
Ref.
y20
2
Ž
.
sections ;30=10
m , the attributes of the
w x
laser-induced fluorescence 4 and a significant dif-
)
ference in reaction cross-section was found with the
isomeric substitution of the alkyl group. This moti-
Corresponding author. Fax: q48 58 341 3175; E-mail:
fizako@univ.gda.pl
0009-2614r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.
Ž
.
PII: S0009-2614 99 00676-4

(
)
184
B. Pranszke et al.rChemical Physics Letters 309 1999 183–190
vated us to study reactivity and electronic energy
partitioning for chemiluminescent reactions in simi-
lar systems. Our work started as a search for steric
effects in reactions of metastable alkaline earth atoms
with propyl iodides; as we found the results for
calcium intriguing, the studies were later extended to
the calcium–propyl bromide and calcium–propyl
chloride systems.
recorded together with the chemiluminescence spec-
tra and their intensities were corrected for the spec-
Ž
tral response of the detection system calibrated with
.
an Osram Wi 17rG tungsten band lamp ; the
N PJ rN D2 number density ratio was later deter-
mined using proper atomic transition probabilities,
given below.
Ž3
.
Ž1
.
The scattering cell was mounted above the beam
source and the effective scattering path length was
xs28"2 mm. Assuming a statistical population of
In this Letter we present experimental results for
the excited alkaline earth atoms colliding with iso-
meric propyl halides:
3
the PJ levels in the discharge and using the radia-
3
tive lifetimes of the P1 states we estimate that the
M) qRX R X ™ MX X 2 Sq qR R ,
1
Ž .
X
X
radiating fractions of the 3PJ reactants in the ob-
Ž
.
Ž
.
Ž
.
served zone were equal to 0.33 and 0.26 for Mg)
™ MX) A 2 P, B 2 Sq, C 2 P qR R ,
2
Ž .
X
Ž
.
Ž
.
)
Ž
and Ca , respectively. The propyl halides Aldrich,
where M) stands for the Mg, Ca, and Sr atoms in
.
purity 99% were put into a Pyrex trap, placed in
Ž3
liquid nitrogen, and pumped. They were ther-
mostated and admitted via a manometer-controlled
metastable states PJ states for all three elements;
1
for Ca and Sr there is also a small fraction of D2
Ž
.
valve Granville-Phillips model 245 to the scattering
cell at pressures up to 0.27 Pa as measured with a
.
Ž
atoms ; MX is an alkaline earth monohalide asterisk
X
.
denotes electronic excitation ; RXsn-C3H7 X, R X
Ž
capacitance manometer MKS Baratron model
si-C3H7 X, where XsI, Br, Cl. Chemilumines-
cence spectra of MX were recorded and compared
for both isomeric targets. Attenuation of those Group
IIA atoms in their metastable states was used to
determine the total collision cross-sections, which
.
120AD-00001RAU . Chemiluminescence spectra
were recorded with a Carl Zeiss Jena SPM-2 grating
Ž
monochromator focal length 0.4 m; 651 lrmm grat-
.
ing, blazed for lB s570 nm and a photon counting
Ž
.
system SR-400 equipped with a cooled Burle
Ž
are upper limits to the reactive cross-sections to
Ž . Ž .
C31034 phototube.
these, routes 1 and 2 bring dominant contribu-
To determine the absolute values of the chemilu-
minescence cross-sections, the contours of atomic
and molecular luminescence were corrected for the
.
tions . Chemiluminescence cross-sections, sCL
Ž .
,
describing path 2 , were measured using the experi-
mental method of Refs. 13,14 .
w
x
spectral response of the detection system. The transi-
1
Ž3
.
tion probability used for Mg was A P1– S0 s225
sy1 average of 10 literature values; see a critical
Ž
1
w
x.
.
Ž3
.
2. Experimental
discussion in Ref. 17 ; for Ca, A P1– S0 s2 460
1
Ž1
Ž
y1
sy1 and A D2– S0 s40 s
averages of data
1
w
x.
Ž3
.
The experimental setup is described elsewhere
collected in 17 . For Sr, where A P1– S0 s52 400
sy1 18 , the upper state is not truly metastable and
we could not use the corresponding line intensity to
w
x
w
x
15 . Briefly, atomic beams were obtained from a
resistively heated oven operated at 900, 1 080, and
1 030 K for Mg, Ca, and Sr, respectively. A dis-
3
monitor the PJ number density as was done in the
charge 8 V, 0.8 A , struck along the beam just
derivation of sCL for Mg) and Ca). A strong
Ž
.
) Ž3
.
above the oven, produced an estimated fraction of
Sr PJ intramultiplet mixing prohibits also the
measurement of total collision cross-sections for
3
Ž
20% of atoms in the metastable PJ states as mea-
3
1
w
x
.
) Ž3
.
sured in Ref. 16 for a similar source . The calcium
Sr P1 via attenuation of the P1– S0 atomic line.
Although we could not extract information on the
and strontium beams contained also a small fraction
of the 1D2 states. For Ca , the N PJ rN D2
Ž3
.
Ž1
.
) Ž3
.
reaction cross-sections of Sr PJ atoms, we ob-
)
tained these data for the Sr 1D2 reactant, using the
) Ž
.
.
number density ratio was equal to 17, as determined
by comparison of intensities of the 3P1–1S0 and
1D2–1S0 atomic lines. The atomic lines were always
1
Ž1
transition probability A D2– S0 s44.7 sy1, calcu-
w
x
lated in Ref. 19 .

(
)
B. Pranszke et al.rChemical Physics Letters 309 1999 183–190
185
w
x
3. Energetics
Atomic energy levels were taken from Ref. 28 . The
bond energies for the hydrogen atoms in normal
propyl iodide and isopropyl iodide are 410 and 398
The energy levels for the systems studied are
given in Fig. 1 in five groups, product states in each
group shifted slightly to the right. The sums of
average translational and internal energies of reac-
w
x
kJrmol 29 , respectively. Therefore the chemilumi-
nescent channels of the alkaline earth hydride prod-
ucts are inaccessible even for the excited state Group
w
x
Ž
tants were estimated as in Ref. 20 and are found to
be between 19 and 25 kJrmol, depending on reac-
IIA metal reactants the ground state hydrides can be
) Ž3 ) Ž
. .
formed in collisions of Mg PJ , Ca 1D2 and
Sr 1D2 . To preserve clarity, the energy levels of
the hydrides are not included in Fig. 1.
) Ž
..
tant combination. Halogen bond strengths of RI and
X
w
x
R I are equal to 226 and 222 kJrmol 21,22 ; of RCl
X
w
x
w
and R Cl are equal to 343 and 339 kJrmol 23 ; of
X
x
RBr and R Br are equal to 289 and 285 kJrmol 23 ,
Ž
respectively for the isomeric forms of a given propyl
4. Results and discussion
halide the dissociation energies are so similar that
the reactant levels for both molecules are drawn as
) Ž3
.
X
For Mg PJ colliding with RI or R I, we have
not observed the expected chemiluminescence in the
.
one line in Fig. 1 . Other dissociation energies used
Ž
.
w
x
Ž
x
.
Ž
.
are: D0 MgI s282 kJrmol 24 , D0 CaI s293
kJrmol 25 , D0 SrI s286 kJrmol 26 , D0 CaCl
range of the MgI A–X transition around 400 nm.
However, it is known that MgI molecules in the
w
x
Ž
.
w
Ž
.
2
w
x
Ž
.
w
x
w x
s405 kJrmol 27 , D0 CaBr s353 kJrmol 25 .
A P state strongly predissociate 15 .
Fig. 1. Energy levels of reactant and product states for the five groups of systems studied. For every group, product states are drawn shifted
X
Ž
.
slightly to the right. Zero on the energy scale corresponds to dissociation into an alkaline earth atom, a halide atom, and the R or R group.
Average translational and internal energies of reactants are included; accessible product chanels lie below corresponding reactant states.
Since the dissociation energies of the normal and branched propyl halide differ by only 4 kJrmol, the levels for RX closely describe those
X
for R X.

(
)
186
B. Pranszke et al.rChemical Physics Letters 309 1999 183–190
X
In collisions of Ca) or Sr) with RI and R I, we
observe CaI or SrI chemiluminescence from the
A 2 P, B 2 Sq and C 2 P states to the ground X 2 Sq
state. For both monohalide product molecules, the
dominant A–X and B–X emissions overlap and we
cannot separate the individual contributions with the
spectral resolution used. The A,B–X spectra for CaI
are shown in Fig. 2, and those for SrI in Fig. 3. At
the target gas pressure of 0.20 Pa, the chemilumines-
X
cence from the reaction of Ca) with R I is ;2.5
times stronger than that for the reaction of Ca) with
RI; for the reactions of Sr), a similar effect is
observed. After normalization of the contours to the
Ž
.
strongest peak, the CaI A,B–X spectra from both
Ž
.
reactions Fig. 2 are very much alike, but not identi-
cal. One can notice that the bands associated with the
B–X chemiluminescence are slightly less intense for
X
the Ca) qR I reaction. For Sr) reactions with both
target molecules, the shapes of the spectra are similar
Ž
.
but not identical see Fig. 3 ; however, the spectral
Ž
.
Ž
Fig. 3. Chemiluminescence spectra of SrI A–X,B–X observed in
X
collisions of Sr) with RI continuous line and R I dotted line .
Spectral resolution: 1.0 nm.
Ž
.
.
congestion prohibits conclusions about the branching
between the A and B states. Chemiluminescence
spectra from the Ca) qpropyl bromide reactions,
shown in Fig. 4, are identical except for a small
difference in the intensity of the DÕsq1 sequence
)
Ž
.
of the CaBr A–X transition. For the Ca qpropyl
Ž
.
chloride reactions spectra in Fig. 5 , the isopropyl
) Ž .
) Ž .
chloride target gives the CaCl A rCaCl B yield
ratio equal to 3.5, compared to 2.6 for the normal
propyl halide target. The isomeric differences in the
ArB branching ratio observed for CaI) and CaCl)
products are probably due to state correlations re-
flecting the geometric and symmetry properties of
the M) qpropyl halide isomer complexes. The state
correlation diagrams for the M) qX2 systems were
w
x
discussed previously in Ref. 30 for various symme-
try groups. Of the systems studied here, M) q
n-C3H7 X is of C1 symmetry, so there are no restric-
tions to charge transfer governing the branching ratio
of the products. For the M) qi-C3H7 X collisions,
where the atom configuration corresponding to C2v
Ž
.
X
Fig. 2. Chemiluminescence spectra of CaI A–X,B–X observed
in collisions of Ca) with RI continuous line and R I dotted
Ž
.
Ž
.
line . Spectral resolution: 1.0 nm. The identified DÕ sequences
Ž
.
band groups for each electronic state are marked above the
spectra in this and the following figures.

(
)
B. Pranszke et al.rChemical Physics Letters 309 1999 183–190
187
one can sometimes clarify chemiluminescence pre-
cursors in cases when both metastable states can
contribute to the observed molecular emission. The
results are collected in Table 1 but they are not
helpful for the latter task, as the values of
st M P1 , st M 1D2 , and st CL are very
similar for a given reactant combination. The data in
Table 1 show that substitution of isopropyl iodide in
place of normal propyl iodide does not change st,
except for Sr), where the values of the total cross-
Ž
) Ž3 ..
Ž
) Ž
..
Ž
.
X
section for an R I target are ;50% higher.
The only result from previous studies with iso-
meric propyl halides concerning differences in reac-
tivity is the 3:2 ratio of reactive cross-sections for an
X
Ž
RI vs. R I target a trend reversed from the one
.
observed here , measured for reactions of ground
w x
state barium with the propyl iodides 4 . Comparing
the results for Ca) and Sr) in Table 1, one must be
aware that there is an important difference between
the Sr) and Ca) atomic beams in our experimental
arrangement: the relatively high probability of spon-
) Ž3
.
taneous emission from the Sr P1 state effectively
Ž
.
Fig. 4. Chemiluminescence spectra of CaBr A–X,B–X observed
X
in collisions of Ca) with RBr continuous line and R Br dotted
Ž
.
Ž
.
line . Spectral resolution: 1.0 nm.
Ž
symmetry is possible although for just a small part
.
of all possible reactant configurations , the local state
correlation diagram for M P qX2 presented in
Fig. 14 of Ref. 30 can be applied. The diagram
indicates that production of the MX B S
impaired in the preferred C2v symmetry, because
there is an adiabatic correlation to the MX A S
) Ž3
.
w
x
2
q
) Ž
.
is
Ž
.
2
) Ž
.
state only. The difference in the branching ratio
observed in our experiment with polyatomic targets
fits this picture.
Ž
.
Ž
.
The CaBr C–X and CaCl C–X spectra were
absent. All spectra shown in Figs. 2–5 are given as
recorded, i.e. without correction for spectral response
Ž
of the detection system this correction is in fact
.
minor in the wavelength range shown . The target
gas pressure, ps0.20 Pa, was identical in all cases.
The band head positions are calculated using spec-
w
x
troscopic constants from Ref. 24 .
We measured the total collision cross-sections via
the attenuation of atomic spectral lines originating
Ž
.
Fig. 5. Chemiluminescence spectra of CaCl A–X,B–X observed
from the 3P1 and 1D2 states, st M , and of the
)
X
Ž
.
in collisions of Ca) with RCl continuous line and R Cl dotted
Ž
.
Ž
Ž
.
.
chemiluminescence, st CL . Comparing these data,
line . Spectral resolution: 1.0 nm.

(
)
188
B. Pranszke et al.rChemical Physics Letters 309 1999 183–190
Table 1
) Ž3
.
.
Total collision cross-sections, st, derived from attenuation of the M
P1 and M 1D2 components in excited atomic beams and from the
) Ž
Ž
.
Ž
.
Ž
.
pressure dependence of the MX A–X, B–X chemiluminescence CL , compared with theoretical refined harpooning cross-sections, sh
y20
all values in 10
m2
.
Ž
Reactive system
Total cross-section
n-C3H7 X target
i-C3H7 X target
a
b
C6
sh
99
st
46"4
st
) Ž3
.
Ž
) Ž3 ..
Mg
P1 qpropyl iodide
st Mg
P
50
42"4
Ž
Ž
..
Žc .
Žc .
st CL A
Ca 3P1, 1D2 qpropyl iodide
) Ž
st Ca
P
90
109
117
125
95"7
120"8
121"8
108"7
122"8
115"7
.
Ž
) Ž3 ..
Ž
) Ž1 ..
st Ca
D
Ž
Ž
..
..
..
..
st CL AqB
Sr 3P1, 1D2 qpropyl iodide
) Ž
st Sr
P
90
126
122
138
.
Ž
) Ž3 ..
Žd.
87"9
86"6
Žd .
136"10
135"9
Ž
) Ž1 ..
st Sr
D
Ž
Ž
st CL AqB
Ca 3P1, 1D2 qpropyl bromide
) Ž
st Ca
P
75
90
111
119
89"6
98"7
99"6
93"6
102"8
103"7
.
Ž
) Ž3 ..
Ž
) Ž1 ..
st Ca
D
Ž
Ž
st CL AqB
Ca 3P1, 1D2 qpropyl chloride
) Ž
st Ca
P
78
95
117
125
100"6
106"8
103"7
97"7
98"8
97"6
.
Ž
) Ž3 ..
Ž
) Ž1 ..
st Ca
D
Ž
Ž
st CL AqB
a
y30
All values in 10y57 m6 kJrmol; calculated using the Slater–Kirkwood approximation; dipole polarizabilities all values in 10
m3 of
.
Ž
Ž
w
x
Ž
.
Ž
.
Ž
.
the propyl halides were taken from Ref. 29 : a C3H7Cl s10.0; a C3H7 Br s9.5; a C3H7 I s11.5; the dipole polarizabilities lower
.
Ž
Ž3
.
limits of the excited alkaline earth atoms were estimated from available oscillator strengths with the exception of Sr PJ , for which the
contribution of the neighboring 4s4d 3DJ state to the polarizability could not be accounted for, as the corresponding oscillator strength is
Ž3
.
Ž3 ..
unknown; we used for the Sr PJ atom the same polarizability as for Ca PJ . The values of polarizabilities used in the calculations of C6
coefficients were in 10
m3 : a Mg PJ s15; a Ca PJ s40; a Sr PJ s40; a Ca D2 s55; a Sr D2 s71.
. Ž Ž Ž Ž Ž
Ž3 .. Ž3 .. Ž3 .. Ž1 .. Ž1 ..
y30
Ž
b
w
x
Calculated using the refined harpoon model 31 , which includes attraction resulting from dispersion forces; theoretical adiabatic electron
w
x
affinities for the normal propyl halides were taken from Ref. 32 .
cChemiluminescence not observed.
d
Not measured because of the strong collisional intramultiplet mixing within Sr 3PJ
) Ž
.
.
w
x
depletes this beam component on the way from the
discharge region to the reaction zone, so primarily
semiempirical calculations 32 give the adiabatic
values of EAsq5, y15, and y36 kJrmol for
C3H7 I, C3H7 Br, and C3H7Cl, respectively. Never-
theless, in the refined harpoon model proposed by
) Ž3
.
only Sr P0, 2 atoms are present in the scattering
w
x
cell. The correlation diagram in Fig. 14 of Ref. 30
indicates that in the C2v symmetry there is a 3B2
correlation to the ground state channel. This could
explain the observed enhancement of the total cross-
section for Sr) qi-C3H7 I. For the Ca) qpropyl
halide reactions, the values of st are rather insensi-
tive to the identity of the halide atom. The total
cross-sections for Mg) reactions indicate a hard
sphere collision. For the Ca) and Sr) reactions, the
experimental values are, however, around 100=
10y20 m2, that is in the range reserved for ‘harpoon-
ing’ collisions. It is known from the literature that
Lijnse 31 , these values lead to harpooning cross-
sections of considerable size for the systems studied
here, because the colliding partners have large elec-
tric dipole polarizabilities, which cause relatively
strong attraction due to dispersion forces. We calcu-
lated the harpooning cross-sections sh for collisions
of Mg), Ca), and Sr) atoms with RX molecules.
The data are collected in Table 1. One can expect
that isopropyl halide has an electron affinity similar
w
x
Ž
to its normal counterpart as it is, e.g., for n- and
w
x.
i-propyl oxide and sulfide 33 , so these values of
sh can be compared also with st for the reactions
Ž
.
Ž
the electron affinities EAs of propyl halides known
X
.
only for the normal molecules are rather small, as
of M) with R I. As can be seen from Table 1, the

(
)
B. Pranszke et al.rChemical Physics Letters 309 1999 183–190
189
) Ž3
.
experimental total cross-sections st are in good
CaX) luminescence was due to Ca PJ atoms
only. This seems justified, as the fraction of
agreement with the refined harpooning cross-sections
Ž
) Ž3
.
) Ž
.
sh with the exception of Mg P1 qC3H7 I, where
Ca 1D2 atoms in our experiment was low – while
other authors find the chemiluminescence cross-sec-
.
the harpooning does not seem to occur .
Ž
Chemiluminescence cross-sections, sCL , are col-
lected in Table 2. The derivation of sCL is straight-
forward only for the C 2 P states of CaI or SrI, since
on energetic grounds they can be formed exclusively
tion for both metastables comparable at least for a
w
x.
propyl iodide target 11 , the small amount of
Ca 1D2 atoms can contribute little to the chemilu-
) Ž
.
w
x
minescence. The results of Refs. 11,34 suggest, that
by attributing all the observed chemiluminescence to
from the reactions of Ca 1D2 or Sr 1D2 atoms,
) Ž
.
) Ž
.
Ž
.
) Ž3
.
respectively. The determination of sCL AqB for
Ca PJ , we probably overestimate the true values
of sCL for these atoms by ;15%. In view of this,
there is very good agreement between the sCL val-
calcium is complicated by possible contributions from
) Ž3
.
) Ž
.
collisions of both, Ca PJ and Ca 1D2 atoms.
There exist procedures to separate the contributions,
as for example by laser depletion of a specific
w
x Ž
ues obtained by us and those in Refs. 11,34 the
latter reference gives sCL for C3H5Br target, where
the R part contains a double bond between carbon
atoms; this should not have an influence on the
w
x
reactant 34 or by variation of the discharge condi-
tions to change the number density ratio of metasta-
w
x
.
bles 35 . Having no access to lasers, we could not
use the first method; we tried to apply the second
one, but without a cathode emission stabilizer, we
failed to obtain reliable results. For this reason we
calculated upper limits to the chemiluminescence
cross-sections, by treating the problem as if the
reactive removal of the Br atom .
Only for Ca) qpropyl bromide are the values of
sCL independent of the isomeric substitution. The
) Ž3
.
X
results for Ca PJ qRCl, R Cl indicate a slightly
) Ž
.
lower rate of CaCl AqB formation for isopropyl
Ž
chloride target instead of an increase of the produc-
Table 2
Exoergicities yD EX in kJrmol and chemiluminescence cross-sections sCL in 10
m2 for the A, B, and C electronic states of the
y20
Ž
.
Ž
.
alkaline earth monohalides
Reactive system
Cross-section for CL
n-C3H7 X target
i-C3H7 X target
yD EX
sCL
yD EX
sCL
Mg 3PJ qpropyl iodide
) Ž
sCL
A
48
52
.
Ž
.
Ža.
Ža.
Ca 3PJ , 1D2 qpropyl iodide
sCL AqB
Ž .
85 A ; 83 B
72
2.3"0.4b, c
0.22"0.05
89 A ; 87 B
76
5.5"1.0b
0.29"0.05
) Ž
.
Ž
C
.
.
.
.
Ž
.
Ž .
Ž
.
Ž .
Ca 1D2 qpropyl iodide
sCL
) Ž
.
Sr 3PJ , 1D2 qpropyl iodide
sCL AqB
Ž .
83 A ; 80 B
51
0.12"0.05
87 A ; 84 B
55
0.17"0.04
) Ž
.
Ž
Ž
.
Ž .
Ž
.
Ž .
Sr 1D2 qpropyl iodide
sCL
C
) Ž
.
Žd.
Žd.
Ca 3P1, 1D2 qpropyl bromide
sCL AqB
Ž .
75 A ; 69 B
42
2.9"0.6b, e
79 A ; 73 B
46
2.9"0.6b
) Ž
.
Ž
Ž
.
Ž .
Ž
.
Ž .
Ca 1D2 qpropyl bromide
sCL
C
) Ž
.
Ža.
Ža.
Ca 3P1, 1D2 qpropyl chloride
sCL AqB
Ž .
71 A ; 61 B
26
2.2"0.4b
75 A ; 65 B
30
1.5"0.3b
) Ž
.
Ž
Ž
.
Ž .
Ž
.
Ž .
Ca 1D2 qpropyl chloride
) Ž
sCL
C
.
Ža.
Ža.
aChemiluminescence was not observed.
b This is an upper limit because sCL was calculated as if all observed CaX AqB chemiluminescence was due to the reaction of
) Ž
.
Ca 3PJ atoms only.
) Ž
.
x
Ref. 11 gives for the Ca 3PJ reaction precursor the value sCL AqB s 1.5"0.8 =10
m2 and for the Ca 1D2 reaction the
) Ž
c
y20
w
) Ž
.
Ž
.
Ž
.
.
y20
value sCL AqB s 2.4"1.0 =10
m2.
Ž
.
Ž
.
) Ž3
.
w
x
d
A strong radiative depletion of the Sr
P1 state prohibits determination of this cross-section by the method of Refs. 13,14 ; however, it
was observed that under identical beam conditions, collisions of Sr) with isopropyl iodide give about twice as much light as those with
normal propyl iodide.
e
Ref. 34 gives sCL AqB s 2.6"0.4 =10
m2 for the Ca 3PJ qC3H5Br reaction and sCL AqB s 5.6"1.2 =10
) Ž
m2
y20
y20
w
x
Ž
.
Ž
.
.
Ž
.
Ž
.
for the Ca 1D2 qC3H5Br reaction.
) Ž
.

(
)
190
B. Pranszke et al.rChemical Physics Letters 309 1999 183–190
) Ž .
tion of CaCl A , as expected from the correlation
diagram in Ref. 30 , this seems only to reflect the
observed lower intensity of emission from the
w x
9
R.W.P. White, D.J. Smith, R. Grice, Chem. Phys. Lett. 193
Ž
.
1992 269.
w
x
w
w
x
Ž
.
10 D.R. Herschbach, Adv. Chem. Phys. 10 1966 311.
x
11 M. Garay, J.M. Orea, A. Gonzalez Urena, Chem. Phys. 207
´
˜
) Ž .
.
CaCl B state for this system . The most dramatic
Ž
.
1996 451.
Ž
.
difference is in sCL AqB for the heaviest combi-
w
x
12 R.-J. Li, K.-L. Han, F.-E. Li, R.-C. Lu, G.-Z. He, N.-Q. Lou,
Ž
.
Chem. Phys. Lett. 220 1994 281.
nations of the reactants, namely for the reactions of
)
w
w
w
x
Ž
.
propyl iodide with Ca) and probably also Sr
13 P.J. Dagdigian, Chem. Phys. Lett. 55 1978 239.
Ž
.
x
Ž
.
14 H. Telle, U. Brinkmann, Mol. Phys. 39 1980 361.
) Ž
.
atoms. In this case, more MX AqB is formed by
reaction with the branched target, where an adiabatic
x
15 P. Kierzkowski, R. Ławruszczuk, A. Kowalski, Chem Phys.
Ž
.
Lett. 225 1994 369.
) Ž .
correlation to the MX A state is possible in the
w
w
w
w
x
16 U. Brinkmann, A. Steudel, H. Walther, Z. Angew. Phys. 22
C2v symmetry. Although the values of st Sr 1D2
..
) Ž
Ž
.
1967 223.
Ž
x
17 A. Kowalski, M. Menzinger, Int. J. Mass Spectrom. Ion
Ž
Ž
..
and st CL AqB in Table 1 are almost identical,
Ž
.
Process. 135 1994 63.
we refrain from the conclusion that the only precur-
x
18 D. Husain, G. Roberts, J. Chem. Soc., Faraday Trans. II 81
) Ž
Ž
.
sors of the SrI AqB chemiluminescence are the
Ž
.
1985 1085.
Sr 1D2 atoms this would give sCL s 74"10 =
x
) Ž
.
Ž
.
19 C.W. Bauschlicher Jr, S.R. Langhoff, H. Partridge, J. Phys.
10y20 m2 for the normal propyl iodide target and
Ž
.
B 18 1985 1523.
y20
w
w
w
x
Ž
.
m2 for isopropyl iodide
20 A. Kowalski, M. Menzinger, J. Phys. Chem. 94 1990 1899.
Ž
.
sCL s 128"17 =10
x
Ž
.
21 S.W. Benson, A.N. Bose, J. Chem. Phys. 39 1963 3463.
.
) Ž .
target . For the MX C states, the sCL values for
isomeric targets seem to reflect the small difference
in exoergicity for the channels.
x
Ž
.
22 A.M. de, P. Nicholas, D.R. Arnold, Can. J. Chem. 62 1984
1850.
w
w
x
Ž
.
23 J.A. Kerr, Chem. Rev. 66 1966 465.
x
24 K.P. Huber, G. Herzberg, Molecular Spectra and Molecular
Structure, vol. 4. Constants of Diatomic Molecules, Van
Nostrand Reinhold, New York, 1979.
Acknowledgements
w
w
w
w
w
w
w
w
w
x
25 P. Kierzkowski, B. Pranszke, P. Wolinski, A. Kowalski,
´
Ž
.
Chem. Phys. Lett. 251 1996 323.
This work was in part supported within the re-
search project BW UG-5200-5-0159-4.
x
26 F. Keijzer, Ph.D. Thesis, Katholieke Universiteit Nijmegen,
1992.
x
27 B. Soep, S. Abbes, A. Keller, J.P. Visticot, J. Chem. Phys.
´
Ž
.
96 1992 440.
x
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