Infra-red cryogenic studies. Part 2.—Effect of matrix environment on hydrogen halide monomers

Abstract

A study has been made of the bands arising from monomeric species of HCl, HBr, and HI in low concentrations in a variety of matrices at 20 K. The presence of hindered rotation, already well established in noble gas matrices, is found also to occur in CH4, CF4 and SFs matrices. Rotation of the HX solute molecule is prevented in Nz, CO, COz, and CzH4 matrices, monomer doublet frequencies being attributed to multiple trapping sites. The formation of a specific complex is believed to occur in an ethylene matrix. The observed matrix-induced frequency shifts of the hydrogen halides are compared with each other and with theoretical values calculated in terms of electrostatic, inductive, dispersive and repulsive interactions.There has been much current interest in the study of rotational motions of small molecules in the condensed phases, hydrogen chloride in particular having been extensively studied. When dissolved in a non-polar liquid the gas-phase rotational fine structure of the fundamental frequency of HCl is replaced by a broad envelope flanking an intense Q branch. When, however, HCl is isolated in a solid argon matrix at low temperatures, discrete rotational lines are observed 3-8. Their reversible variation of intensity with changes of temperature are characteristic of changes in population of low-lying energy states, and bands have been assigned to R(O), R(1) and P(l) transitions corresponding to quantized rotational motion of HC1 in the host lattice. A feature corresponding to a Q branch is also observed. This is similar to that reported by Vodar et aL9 in HCl or HBr mixtures pressurized with Ar or with N2.Similar P, Q, and R features are found for H(D)Cl in other 3* 5-8* l o * l 1 noble gas matrices and also for HF12, H(D)Br 3* 5 * 7 * 8 * and HI 7* * in noble gas matrices.Apart from HCl and DCl in SF6 the only other matrix which has been utilized is N2. Whilst hindered rotation is also considered l3 to exist in SF,, there is a divergence of opinion as to whether or not it occurs in N2. Pimentel et aZ.14 and Bowers et aL8* l 2 from their observation of singlet monomeric frequencies conclude that rotation does not take place in a N2 matrix, but Shurvell et aZ.159 l6 have presented evidence which suggests that hindered rotation may exist.Although the hindered rotation model is generally acceptable in that it accounts for the overall features it is unable to account precisely for the matrix perturbations of the R(0)-P(1) rotational spacings. By extending the range of host matrices, as described in this study, it was hoped to throw some light on the factors which contribute to these perturbations. EXPERIMENTAL Details are described in part 1.

HXeI and HXeH in Ar, Kr, and Xe matrices: Experiment and simulation

“…This band can be assigned to the HI···Xe complex (shift of −4 cm −1 from the band of non-rotating HI at 2226 cm −1 ). 15,19 This assignment is consistent with the case of an Ar matrix showing a normal matrix shift of this band.…”

Matrix effect on vibrational frequencies: Experiments and simulations for HCl and HNgCl (Ng = Kr and Xe)

“…4,[22][23][24][25] The R(0) branch produces the strongest bands at 2900, 2887.5, 2872.5, and 2858 cm −1 in Ne, Ar, Kr, and Xe matrices, respectively, red-shifted from the gas-phase value of 2905.7 cm −1 (for the main isotope 35 Cl). The H 37 Cl absorptions are ∼2 cm −1 lower in energy.…”

“…43 The MP4 correlation energy correction consists of the MP2, MP3(D), MP4(SDQ), and MP4(T) corrections, which is known to describe well the dispersion interactions. 44,45 While the MP2 method scales as nN 4 where n is the number of the occupied and correlated molecular orbitals and N is the total number of the basis functions, the third-order correction (MP3(D)) scales as n 2 N 4 and the fourth-order correction with single, double, and quadruple substitutions (MP4(SDQ)) scales as n 3 N 3 . Because the scaling of MP4(T) is n 3 N 4 , the energy calculations with MP4(SDQ) are much faster than with MP4(SDTQ).…”

“…The classical example of this trend is reported for the stretching frequencies of hydrogen halides HY, all showing the order ν(gas) > ν(Ne) > ν(Ar) > ν(Kr) > ν(Xe). 4 These matrix-induced shifts can be qualitatively understood in terms of solvation a) Present address: Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA. b) E-mail: leonid.khriachtchev@helsinki.fi of a molecule in a polarizable medium.…”

Matrix site effects on vibrational frequencies of HXeCCH, HXeBr, and HXeI: a hybrid quantum-classical simulation

“…1,[17][18][19] These results are in contrast to the ''normal'' order observed for HCl: n(Xe) o n(Kr) o n(Ar) o n(Ne) o n(gas). 20,21 The vibrational spectroscopy measurements of HXeCCH and HXeBr in various noble-gas matrices also revealed the unusual vibrational shifts of the H-Xe stretching frequency in the order n(Ne) o n(Xe) o n(Kr) o n(Ar), 1,17,[22][23][24][25] which is the same as that observed for HXeCl.…”