Infrared spectra and molecular dynamics simulations of cis-HONO isomer in an argon matrix

Article abstract of DOI:10.1016/S0022-2860(02)00071-6

Temperature dependent infrared spectra of cis-HONO trapped in an argon matrix are presented. All observed cis-HONO fundamental bands appear as doublets in the spectra. Both components of each doublet show reversible temperature broadening. Molecular dynamics simulations of cis-HONO trapping in an argon matrix suggest that the molecule is trapped in a one-atom substitutional cage in solid argon; no evidence of non-equivalent trapping sites was found. Experimental and theoretical results are discussed.

Full text of DOI:10.1016/S0022-2860(02)00071-6

Journal of Molecular Structure 611 ꢀ2002) 95±102
www.elsevier.com/locate/molstruc
Infrared spectra and molecular dynamics simulations of cis-HONO
isomer in an argon matrix
a
Tadeusz Talik , Konstantin G. Tokhadze , Zo®a Mielke
b
a,*
a
Faculty of Chemistry, Wrocøaw University, F. Joliot-Curie 14, 50-383 Wrocøaw, Poland
Institute of Physics, St Petersburg University, 198904 St Petersburg, Russian Federation
b
Received 2 January 2002; accepted 31 January 2002
Abstract
Temperature dependent infrared spectra of cis-HONO trapped in an argon matrix are presented. All observed cis-HONO
fundamental bands appear as doublets in the spectra. Both components of each doublet show reversible temperature broadening.
Molecular dynamics simulations of cis-HONO trapping in an argon matrix suggest that the molecule is trapped in a one-atom
substitutional cage in solid argon; no evidence of non-equivalent trapping sites was found. Experimental and theoretical results
are discussed. q 2002 Elsevier Science B.V. All rights reserved.
Keywords: Nitrous acid; Matrix isolation; Infrared spectra; Molecular dynamics simulations
1
. Introduction
molecule in the two-atom cage. Correlating these results
with experimental data, we assumed that the observed
differences in temperature behaviour of the components
of trans-HONO fundamental bands may be attributed to
differences in mobility of the molecule trapped in these
two types of cages.
This paper presents results of application of similar
procedure to cis-HONO. The infrared spectra of cis-
HONO trapped in argon matrices were measured and
molecular dynamics simulations of trapping of the cis-
HONO molecule in argon matrices were performed.
The paper presents the experimental spectra, the
molecular dynamics simulations and a discussion of
both experimental and theoretical results.
In our recent paper, we presented the results of mole-
cular dynamics simulations of formation and properties
of argon matrices containing the trans-HONO molecule
[
1]. The calculations were stimulated by striking
temperature behaviour of infrared spectra of matrix-
isolated trans-HONO. The fundamental bands of
trans-HONO consist of two or three components. One
component of a doublet or two components of a triplet
show much stronger broadening with temperature than
thesecondorthirdcomponent. Thechangesare comple-
tely reversible with temperature. Performed simulations
suggested that the trans-HONO molecule is trapped in
two kinds of cages in solid argon: a one-atom substitu-
tional cage or a two-atom substitutional cage. Reorien-
tational mobility of the molecule in the one-atom cage
was found tobesigni®cantly greater than mobilityofthe
2. Matrix isolation studies
2
.1. Experimental
*
Corresponding author. Tel.: 148-71-3204475; fax: 148-71-
282348.
E-mail address: zm@wchuwr.chem.uni.wroc.pl ꢀZ. Mielke).
3
The source of HONO in our experiments was
0022-2860/02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-2860ꢀ02)00071-6

96
T. Talik et al. / Journal of Molecular Structure 611 ꢀ2002) 95±102
Fig. 1. Temperature dependence of the infrared spectra of cis-HONO in an argon matrix. All four observed cis-HONO fundamental bands are
presented.
NH NO . Two methods of deposition were used to
4
changing the initial pressure of the argon gas. In
the second method, HONO and NH were evapo-
2
isolate HONO in argon matrices. In the ®rst
method, argon gas was added to a bulb containing
small amount of solid NH NO to obtain HONO,
3
rated into the vacuum vessel of the cryostat from
a small glass tube containing solid NH NO .
4
2
4
2
NH3 and Ar mixture. After passing through a
stainless steel tube with walls pre-saturated with
HCl, the mixture was deposited onto a sample
holder. The HONO:Ar ratio was controlled by
Simultaneously, argon gas was introduced into
the cryostat in such a way that it mixed with
HONO and NH mixture in the vacuum chamber.
3
The HONO:Ar ratio was controlled by changing

T. Talik et al. / Journal of Molecular Structure 611 ꢀ2002) 95±102
97
Table 1
temperature is raised; in consequence, the bands are
poorly resolved at 30 K. The changes are completely
reversible with temperature; the spectrum recorded
after cooling the matrix to 11 K is almost identical
to the original low-temperature spectrum.
2
1
21
Frequencies ꢀn, cm ), FWHM ꢀDn1/2, cm ) and relative intensi-
ties of resolved bands of cis-HONO in the spectra of matrices at 12
and 25 K
Assignment 12 K
25 K
In order to determine the temperature behaviour
more precisely, the bands were numerically resolved
into two components each. The Lorentzian contours
allowed us to reproduce satisfactorily the experi-
mental spectra. Results of the band decomposition
are summarized in Table 1. In contrast to trans-
HONO, for cis-HONO both component of each
doublet show similar broadening with temperature.
However, just as it was observed for trans-HONO,
no substantial changes in relative intensities of
components of the same doublet were found.
a
a
n
Dn1/2
B
n
Dn1/2
B
n
OH stretch
1
3412.4 ꢀ2) 0.7
0.3 3412.1 ꢀ2) 1.5
0.7 3410.8 ꢀ2) 1.5
0.2
0.8
3410.9 ꢀ2) 0.9
n 1634.0 ꢀ2) 0.4
NyO stretch 1632.7 ꢀ2) 0.4
2
0.3 1633.8 ꢀ2) 0.8
0.7 1632.8 ꢀ2) 0.7
0.2
0.8
n
N±O stretch
4
852.8 ꢀ2) 0.8
850.1 ꢀ2) 0.9
0.2 851.9 ꢀ2) 1.1
0.8 849.7 ꢀ2) 1.1
0.15
0.85
n
OH torsion
6
639.3 ꢀ2) 0.7
638.3 ꢀ2) 0.8
0.3 639.2 ꢀ3) 1.4
0.7 638.1 ꢀ2) 1.6
0.2
0.8
a
B expresses the intensity contribution of a particular component
All above observations are independent of the
method of matrix deposition. Variation of deposition
temperature had only minor effect on the spectra.
to the overall intensity of absorption for a fundamental.
the ¯ow rate of the argon gas. The details of both
methods are described in our earlier papers [1±4].
Matrices were deposited onto a gold-plated copper
mirror attached to a temperature controlled closed-
cycle helium refrigerator ꢀAIR Products Displex
3
. Molecular dynamics simulations
3.1. Description of simulations
2
02A). Temperature was measured with a calibrated
silicon diode sensor placed between the Displex cold
mirror and the copper block. Estimated error in
temperature measurement is less than ^1 K.
Temperatures of deposition were 12, 17 and 20 K.
The HONO:Ar ratio was varied between 1:600 and
Formation of an argon matrix containing trapped
cis-HONO molecule was simulated using the mole-
cular dynamics approach similar to those applied by
Fraenkel and Haas [5±8] and Cruz and L o pez [9,10].
Thematrixwasdepositedonaseedcrystal,whichforces
creation of appropriate crystal structure and provides a
way to drain excess energy carried by depositing
species. The seed crystal consisted itself of two parts:
a `soft' seed crystal of 200 argon atoms ꢀfour {001} fcc
layers of 50 argon atoms each) and a `rigid' seed crystal
of 100 argon atoms ꢀtwo {001} fcc layers of 50 argon
atomseach).Newmatrixmaterialwassuppliedfromthe
positive direction of z-axis towards the surface of the
soft seed crystal.
One cis-HONO molecule and 350 argon atoms
were added to the system one by one, allowing
constant time interval between adding species. The
temperature of the soft seed crystal was kept at 15 K
by periodic scaling of momenta of the soft seed crystal
argon atoms. Species were added to the system from
two reservoirs: a reservoir of 350 argon atoms of
temperature 298 K ꢀall atoms added) and a reservoir
of 350 cis-HONO molecules of temperature 298 K
1
:1000. Infrared spectra were recorded in the re¯ec-
21
tion mode with resolution of 0.13 and 0.26 cm on a
Bruker 113v FTIR spectrometer equipped with the
MCT detector. The spectra were measured at 12, 15,
2
0, 25 and 30 K.
2
.2. Results
Only four bands of cis-HONO, namely bands corre-
sponding to n OH stretch, n NyO stretch, n N±O
1
2
4
stretch and n6 OH torsion were observed in the
infrared spectra of cis-HONO isolated in an argon
matrix. Fig. 1 presents all four bands in function of
temperature. As was reported previously for trans-
HONO [1], the bands of cis-HONO show distinct
changes with temperature. At 12 K, all four bands
appear as doublets with well-resolved components.
Both components of the doublet broaden when

98
T. Talik et al. / Journal of Molecular Structure 611 ꢀ2002) 95±102
Fig. 2. Schematic presentation of the cis-HONO molecule trapped in the one-atom substitutional cage. Larger pairs of circles indicate argon
atoms in the plane in which the molecule is placed and smaller ones refer to argon atoms in the plane below. In each pair of circles, outer one
indicates the actual equilibrium position of the argon atom and the inner one, the position of the argon atom in the ideal argon crystal lattice.
ꢀ
only one molecule added). Two orders of adding
computer. All details, including setting initial condi-
tions and simulation timing, can be found in our
previous paper [1].
species were used: ꢀ1) the HONO molecule was
added as ®rst and followed by 350 argon atoms
ꢀ
0 1 1 1 350 model), ꢀ2) 50 argon atoms were
added before the HONO molecule, which was
followed by 300 argon atoms ꢀ50 1 1 1 300 model).
Obtained matrices were cooled to 10, 5, 1 and 0.1 K
and heated to 20, 25, 30, 35 and 40 K by periodic
scaling of momenta of the soft seed crystal atoms
and all deposited argon atoms.
3
.2. Matrix structure
In the deposition process, gradual ABAB¼ growth
of the matrix material layers results in reproduction of
the fcc structure of the seed crystal. As it was
observed previously [1], formation of each of succes-
sive layers begins before completion of a previous
layer, what may lead to presence of crystal lattice
defects. In fact, some one-atom defects were observed
in our simulations. From 8 to 10 layers of argon atoms
were deposited, of which 3±5 are closed and 4±8 form
the surface of the matrix. Some deformations of the
argon crystal lattice were observed in the vicinity of
the defects and on the matrix surface.
When the matrix is heated to 40 K, the number of
closed layers usually increases and the number of
surface layers decreases. Crystal lattice defects lying
near the matrix surface may disappear in this process.
It leads to more ordered matrix structures, with lower
total number of layers and fewer defects.
The rigid body approach was used for the cis-
HONO molecule. The geometry of the molecule
was chosen to be identical to the equilibrium
geometry from Guan et al. [11] intramolecular
HONO potential. Molecular orientation was described
by means of the quaternion ꢀEuler±Rodrigues) para-
meters [12±14]. Periodic boundary conditions were
used in the xy-plane. Interatomic interactions were
described by the Lennard±Jones 12-6 potentials
with parameters taken from literature [10,15] and
spherical truncation with maximum cut-off distance
allowed by periodic boundary conditions. Equations
of motion were solved by the standard leap-frog
algorithm [16] for translational motion and by the
quaternion leap-frog algorithm [17] for rotational
motion. Time step was 1 fs.
In all cases, the cis-HONO molecule was trapped in
the formed matrix. In contrast to our previous
study concerning trans-HONO, where one-atom and
Calculations were performed on the IBM SP2

T. Talik et al. / Journal of Molecular Structure 611 ꢀ2002) 95±102
99
two-atom substitutional cages were observed, only
one-atom substitutional cages were obtained in
current simulations. In the case of the 0 1 1 1 350
model, the trapping cage was located in the ®rst
deposited layer, while in the case of the
[1], it is worth noting, however, that the rotation of
the OH fragment of the cis-HONO molecule around
the central ON bond by 1808 leads to situation closely
resembling the trans-HONO molecule in the one-
atom cage.
5
0 1 1 1 300 model, it was located in the ®rst or
The argon crystal lattice is deformed to some extent
around the trapped molecule. Most pronounced
perturbations are observed in the molecular plane.
Two argon atoms closest to the terminal OH and
NO molecular fragments are noticeably pushed
outwards the trapping cage. Two other closest argon
atoms are slightly shifted towards the cage. Smaller
shifts, in general towards the trapping cage, are
observed in two adjacent argon atom planes parallel
to the molecular plane. Distortions are propagated in
the crystal lattice with magnitude decreasing with
increasing distance from the trapped molecule ꢀsee
Fig. 2).
second deposited layer with similar probabilities.
The trapping cage was covered by up to four closed
layers of argon atoms and ꢀpossibly) several not
closed layers. The argon crystal lattice was deformed
to some extent near the trapping cage.
3
.3. Trapping sites
At suf®ciently low temperature, the position ꢀposi-
tion of the centre of mass) and orientation of the
trapped cis-HONO molecule are practically ®xed.
One may say that the molecule occupies its trapping
site. There are 24 trapping sites for the cis-HONO
molecule in the one-atom substitutional cage. The
molecule lies in xy, xz- or yz-plane and the line
connecting terminal O and H atoms is nearly parallel
to the line bisecting the angle between the coordinate
system axes ꢀsee Fig. 2). The centre of mass of the
molecule is located close to the missing argon atom
position, with slight shift along the latter of above-
mentioned lines in a direction opposite to the direction
pointed by the H atom. Consider three axes a, b, c
parallel to the coordinate system axes and passing
through the missing argon atom equilibrium position.
Suppose that the molecule is located in the ab-plane.
Rotation around axis a or b by 1808, rotations around
axis c by 90, 180 and 2708, and combinations of these
two types of rotations ꢀrotation around axis a or b 1
rotation around axis c) transform the molecule to other
trapping sites in the ab-plane. Rotation around axis a
b y 9 08 transforms the molecule to another trapping
site in the ac-plane and rotation around axis b by
3.4. Matrix dynamics
As can be expected, argon atoms oscillate around
their equilibrium positions in the crystal lattice.
Magnitude of these oscillations increases with
increasing temperature. The equilibrium positions
may be different from positions in the ideal crystal
lattice in the case of structural defects, on the matrix
surface and in the vicinity of the trapping cage. As it
was observed in our previous study [1], after deposi-
tion at 15 K some argon atoms on the surface of the
matrix change their position in the crystal lattice to
another surface position. Certainly, particularly at low
temperatures, it takes some time before the surface of
the matrix reaches equilibrium. Changes of this type
are more pronounced at higher temperatures leading
to described changes in matrix structure.
At 0.1, 1, 5 and 10 K, the cis-HONO molecule
occupies one of its trapping sites. At 10 K, isolated
jumps between different trapping sites are observed,
however, it is a rare event on the simulation time
scale. At 15 K, this motion is quite easily observed.
When temperature is raised, the frequency and rate of
jumping increases. At a given temperature, jumps
between trapping sites for the cis-HONO molecule
in the one-atom cage are less frequent than for the
case of the trans-HONO molecule in the one-atom
cage, but more frequent than for the case of the
trans-HONO molecule in the two-atom cage [1].
9
08 transforms the molecule to another trapping site
in the bc-plane. All other sites with the molecule in the
ac- and bc-planes may be reached by rotation analo-
gous to the rotations transforming molecule between
trapping sites in the ab-plane. All the above-
mentioned rotations are the symmetry operations of
the ideal argon crystal lattice, so all trapping sites are
equivalent. The orientation of the cis-HONO mole-
cule in the one-atom cage is similar to the orientation
of the trans-HONO molecule in the two-atom cage

100
T. Talik et al. / Journal of Molecular Structure 611 ꢀ2002) 95±102
During the time period when the cis-HONO mole-
and placed on the matrix surface. Then, the simulation
was carried out to the end. Obtained results were inde-
pendent of the method of matrix preparation and on
the choice of removed argon atom. The matrices were
cooled and heated in the described manner.
cule occupies one of its trapping sites, the centre of
mass of the molecule ¯uctuates around the equili-
brium position characteristic for this trapping site. In
contrast to the trans-HONO molecule in both types of
cages, no noticeable anisotropy of this motion was
observed in the case of the cis-HONO isomer in the
one-atom cage. Also, orientation of the molecule
shows ¯uctuations around equilibrium orientation
corresponding to the trapping site. As can be
expected, degree of position and orientation ¯uctua-
tions increases with increasing temperature. During
the jump between two trapping sites, concerted
changes of molecular orientation and position of the
centre of mass are observed. Simultaneously, re-
organization of the trapping cage takes place to
conform to new orientation of the molecule.
Positions and orientations of the cis-HONO mole-
cule corresponding to trapping sites in the two-atom
substitutional cage were similar to those found for the
trans-HONO molecule in the same type of cage [1].
The cis-HONO molecule was located close to one of
the missing argon atom positions, with the terminal H
atom located near the second missing argon atom
position. Possible orientations of the cis-HONO mole-
cule were slightly changed with respect to the trans-
HONO analogue to account for new shape of the
molecule. Motional characteristics of the cis-HONO
molecule in the two-atom cage were also similar to the
trans-HONO case [1]. However, reorientational
mobility of the cis-HONO molecule was found to be
even lower than it was for the case of the trans-HONO
molecule in the two-atom cage. The centre of mass of
the cis-HONO molecule oscillates around equilibrium
position characteristic for this trapping site, with
somewhat greater freedom along the cage with respect
to the perpendicular directions. Jumps of the molecule
to the other missing argon atom position were
observed at higher temperatures. They were not
frequent, but the molecule could spend considerable
amount of time in the new position.
3
.5. Remark concerning matrix structure
Some matrix structure deformations were observed
along the z-axis direction. At lower temperatures, the
matrices were slightly ¯attened, and at higher
temperature expanded. It causes slight differences in
orientation of the molecule corresponding to trapping
sites differing in placement of the molecule relative to
the z-axis. The effect was neglected for sake of simpli-
city in the discussion presented above, as well as in
our previous paper concerning trans-HONO [1]. The
angle data presented therein refer to the molecule
lying in the xy-plane, where the in¯uence of these
distortions is the smallest.
4. Discussion
3
.6. cis-HONO molecule in the two-atom cage
The spectra of cis-HONO in argon matrices show
In addition to described simulation approaches, we
similar features as the spectra of trans-HONO isomer.
All four fundamental modes that are identi®ed in the
spectra appear as doublets. All doublets show rever-
sible temperature broadening, like the trans-HONO
absorptions. However, temperature behaviour of the
absorptions due to the cis-HONO molecule is slightly
different from behaviour of the corresponding absorp-
tions of the trans-HONO isomer. In the case of the
trans-HONO isomer, one component of the doublet
observed for n NyO, n N±O stretches and n OH
decided to examine behaviour of the cis-HONO mole-
cule trapped in the two-atom substitutional cage.
Three methods of placing the cis-HONO molecule
in the two-atom cage were used: ꢀ1) immediately
after matrix deposition, the trans-HONO molecule
was replaced by the cis-HONO analogue without
changing its position and orientation data, ꢀ2) the
trans-HONO molecule was replaced by cis-HONO
analogue without changing its orientation data, but
the position was changed to the second missing
argon atom position, ꢀ3) immediately after matrix
deposition, one of argon atoms closest to the cis-
HONO molecule in the one-atom cage was removed
2
4
6
torsion, and two components of the triplet observed
for the n OH stretch broadened more strongly with
1
temperature than the other component of the doublet
or triplet. The relative intensities of the two or three

T. Talik et al. / Journal of Molecular Structure 611 ꢀ2002) 95±102
101
components did not show pronounced changes with
temperature. In the case of cis-HONO, both compo-
nents of the observed doublets exhibit similar broad-
ening with temperature ꢀsee Table 1). The relative
integrated intensities of the two components of the
doublets do not show distinct changes with tempera-
ture, just like in the case of trans-HONO.
The spectral data for trans-HONO were correlated
with molecular dynamics simulations that showed
existence of two types of trapping cages in an argon
matrix, namely the one- and two-atom substitutional
cages. The bands showing larger temperature broad-
ening were assigned to the trans-HONO molecule in
the one-atom cage, with more pronounced reorienta-
tional motion, and those showing less sensitivity to
temperature to the trans-HONO isomer occupying
the two-atom cage.
In contrast to trans-HONO, only one-atom
substitutional cages were observed in simulations
for the cis-HONO molecule. This result is in agree-
ment with more `compact' shape of the cis-HONO
molecule. At a given temperature, reorientational
mobility of the cis-HONO molecule in the one-
atom cage was found to be slower than for the
trans-HONO molecule in the one-atom cage, but
faster than for the trans-HONO molecule in the
two-atom cage. The nature of reorientation of the
cis-HONO molecule in the one-atom cage is
different from the reorientation of the trans-
HONO molecule in the same type of cage. In
both cases, reorientation is restricted to jumping
between equivalent sites differing in molecular
orientation. However, even at low temperatures,
reorientational jumps of the cis-HONO molecule
are not limited to rotation around one axis, as it
was observed for the trans-HONO molecule below
of the cis-HONO molecule in the two-atom cage, the
molecule was placed in such a cage and molecular
dynamics simulations at different temperatures were
performed. The calculations showed that reorienta-
tional mobility of the cis-HONO molecule in the
two-atom cage is signi®cantly lower than in the one-
atom cage. This is not consistent with experimental
infrared spectra that show similar broadening of both
components of cis-HONO bands with temperature
ꢀassuming that mobility is the main reason of tempera-
ture broadening). Due to `compactness' of the cis-
HONO molecule, formation of the two-atom cages
for this molecule is questionable. Even for more
`spacious' trans-HONO molecule, probability of
formation of the two-atom cage was found to be
small. There is another hypothetical possibility,
which should be mentioned. The cis-HONO molecule
may occupy two non-equivalent sites in the one-atom
cage, with only one site detected in our simulations
due to inaccurate description of argon atom±HONO
molecule interactions. Then, the splitting and
temperature behaviour of cis-HONO bands may be
explained by motional collapse [18]. The changes of
cis-HONO bands with temperature do not exclude
such an explanation. However, common spectral
features observed for two HONO isomers suggest
that the origin of band splitting and temperature
broadening is the same for both isomers. The tempera-
ture changes of n OH stretch band exclude motional
1
collapse in the case of trans-HONO. If the above
suggestion is correct, then motional collapse should
be excluded also for cis-HONO. For the same reason,
the explanation suggested for trans-HONO in our
previous paper [1] is also questionable. The simula-
tions do not con®rm the existence of the two-atom
substitutional cages for cis-HONO in solid argon
and, for the case of trans-HONO, probability of
formation of such a cage is not enough high to account
for spectral characteristics of the trans-HONO funda-
mental absorptions [1].
We are considering two other possible reasons of
splitting and temperature behaviour of matrix-
isolated HONO infrared bands. The ®rst is in¯u-
ence of the matrix surrounding. In fact, atoms
constituting the HONO molecule are signi®cantly
lighter than the argon atom, so there is a possibility
of frequency modulation of the HONO molecule
modes by the argon crystal lattice [19]. The other
3
5 K [1].
The simulations did not con®rm the existence of
two-atom substitutional cages for cis-HONO in an
argon matrix. There is a hypothetical possibility that
the absence of this type of cages is a consequence of
the applied matrix formation model. If both one- and
two-atom substitutional cages exist in argon matrices
containing cis-HONO, then there is a chance that the
structure and temperature behaviour of the bands of
cis-HONO can be explained in a way analogous to
suggested by us for the case of trans-HONO. In
order to get some information concerning behaviour

102
T. Talik et al. / Journal of Molecular Structure 611 ꢀ2002) 95±102
possibility is that the matrix is polycrystalline with
crystallites of two different structures, probably fcc
and hcp [20]. The HONO molecules are then
trapped in two different argon lattice environments,
possibly with different mobility for trans- and cis-
forms. The structure and reversible temperature
changes of the infrared bands are consistent with
both explanations. It is worth noting that even hcp
structure alone may explain observed spectral
features, provided that it can lead to two non-
equivalent trapping sites. Further simulation
approaches, including calculations for hcp and fcc
structures with different lattice planes facing the
depositing material and calculations for non-rigid
HONO molecule model are necessary to clarify
the situation. We plan to perform such calculations
in the near future.
Acknowledgements
T.T. gratefully acknowledges the Wrocøaw Centre
of Networking and Supercomputing for providing
computer time and facilities.
References
[
1] T. Talik, K.G. Tokhadze, Z. Mielke, Phys. Chem. Chem. Phys.
ꢀ2000) 3957.
2
[2] Z. Mielke, K.G. Tokhadze, Z. Latajka, E. Ratajczak, J. Phys.
Chem. 100 ꢀ1996) 539.
[
3] Z. Mielke, Z. Latajka, J. Koøodziej, K.G. Tokhadze, J. Phys.
Chem. 100 ꢀ1996) 11610.
[
4] Z. Mielke, T. Talik, K.G. Tokhadze, J. Mol. Struct. 484 ꢀ1999)
2
07.
[5] R. Fraenkel, Y. Haas, J. Chem. Phys. 100 ꢀ1994) 4324.
[6] R. Fraenkel, Y. Haas, Chem. Phys. Lett. 220 ꢀ1994) 77.
The most striking feature of the spectra of
trans-HONO in solid argon was the splitting and
temperature behaviour of the absorption in the OH
stretch region [1]. The absorption consisted of
three components; two components were assigned
to trans-HONO molecules occupying one-atom
cages and the third component to molecules
trapped in two-atom cages. In contrast to trans-
HONO spectra, in the spectra of cis-HONO
isomer, a doublet is observed for the OH stretch,
like for the three other fundamentals. The different
spectroscopic characteristics of the trans- and cis-
HONO isomers in this region can be reasonably
justi®ed. Weak intramolecular hydrogen bonding
that is present in the cis-HONO isomer, as well
as more compact shape of this molecule, effect the
interaction potential between the HONO molecule
[
[
7] R. Fraenkel, Y. Haas, Chem. Phys. 186 ꢀ1994) 185.
8] R. Fraenkel, S. Kahana, Y. Haas, Ber. Bunsenges. Phys.
Chem. 99 ꢀ1995) 412.
[
9] J. Cruz, G.E. L o pez, J. Chem. Phys. 104 ꢀ1996) 4294.
[
10] J. Cruz, G.E. Lopez, J. Chem. Phys. 104 ꢀ1996) 4301.
[11] Y. Guan, G.C. Lynch, D.L. Thompson, J. Chem. Phys. 87
1987) 6957.
Â
ꢀ
[
12] L.C. Biedenharn, J.D. Louck, Angular Momentum in
Quantum Physics, Theory and Applications, Addison-Wesley,
Reading, MA, 1981.
[
13] D.J. Evans, Mol. Phys. 34 ꢀ1977) 317.
[14] D.J. Evans, S. Murad, Mol. Phys. 34 ꢀ1977) 327.
[
[
[
15] P.M. Agrawal, D.L. Thompson, L.M. Raff, J. Chem. Phys. 102
1995) 7000.
ꢀ
16] M.P. Allen, D.J. Tildesley, Computer Simulation of Liquids,
Clarendon Press, Oxford, 1990.
17] D. Fincham, Leapfrog Rotational Algorithms, Daresbury
Laboratory Preprint DL/SCI/P755T.
[18] B.I. Swanson, L.H. Jones, in: J.R. Durig ꢀEd.), Vibrational
Spectra and Structure, vol. 12, Elsevier, Amsterdam, 1983,
pp. 2±67 and references cited therein.
[
10] and its microenvironment. One might expect
that the interaction of `sticking out', non-bonded
OH group of trans-HONO with surrounding argon
lattice will be stronger than the interaction of the
OH group involved in weak intramolecular
hydrogen bonding as in the case of cis-HONO.
[
19] P.M. Agrawal, D.C. Sorescu, R.D. Kay, D.L. Thompson, L.M.
Raff, J.B. Conrey, A.K. Jameson, J. Chem. Phys. 106 ꢀ1996)
2
686.
[20] B.W. van de Waal, G. Torchet, M.-F. de Feraudy, Chem. Phys.
Lett. 331 ꢀ2000) 57.