Infra-red cryogenic studies. Part 1.—Hydrogen halide multimers

Abstract

Infra-red spectra are reported of HCl, HBr and HI in argon and other matrices at 20 K. Studies have been made over a wide concentration range from matrix/absorber ratio 2000 to 50 which, together with diffusion (" warm-up ") experiments, enable an interpretation to be offered of the complex pattern of frequencies. The first two intense association bands which arise are assigned to cyclic dimers and trimers respectively. Bands are also assigned to various multimeric species and the frequencies compare favourably with values calculated on the basis of a model based on that proposed by Keyser and Robinson.

The vibrational spectra of molecular ions isolated in solid neon. XIII. Ions derived from HBr and HI

“…The 2 ϩ term value 31 of gas-phase ͑H 35 Cl͒ 2 is 2854.06 cm Ϫ1 , and the corresponding absorption appears at 2842.2 cm Ϫ1 in a neon matrix 18 and at 2818 cm Ϫ1 in an argon matrix. 27,28 This comparison suggests that the ͑HBr͒ 2 absorption probably occurs at a considerably higher frequency in a neon matrix than in an argon matrix and supports the assignment of the neon-matrix absorptions near 2520 cm Ϫ1 to ͑HBr͒ 2 . As will be shown, an analogous absorption pattern was observed in the DBrstretching region in this study, consistent with such an assignment.…”

Effect of Deposition Temperature on the Mobility of Matrix-Isolated Species: HBr in Xenon

“…The separation of 22 cm -1 between the R(0) and P(1) absorption is in good agreement with a separation of 19 cm -1 in argon. 8 The weak Q branch absorption at 2520.1 cm -1 is more prominent in the spectrum of the matrix deposited at 28 K than at higher temperatures (see Figure 3). A number of absorptions due to HBr dimers and various higher-order multimers and their isomers have been identified in lighter rare gases.…”

“…In principle, molecules formerly in lower energy trap sites could be so mobile that they form "high polymers" or even clusters of "solid" HBr. Absorptions for these species have been identified in prior studies, 8 and there is no evidence for their formation at the different deposition temperatures under experimental conditions. In addition, there is no significant depletion of parent for higher temperature deposition relative to lower temperature deposition as would be required by this explanation.…”

Investigation of the ground vibrational state structure of H35Cl trimer based on the resolved K, J substructure of the ν5 vibrational band

“…This trimer was initially studied by Barnes et al in 1969 using argon matrix isolation spectroscopy at 20 K. 9 Recently, matrix isolation spectra of the lI5 band in (HClh in Ar and Ne were reported to be at 2787 and 2801.5 cm-I , respectively,1O-12 and the gas phase vibration frequency of this band was predicted by Andrews and BohnI2 to be 2816±3 em-I. Ab initio calculations for the HCI trimer by Latajka and Scheiner lead to the conclusion that the optimum geometry for the HCI trimer is a planar cyclic equilibrium structure with C 3h symmetry.13 A cyclic structure for the HCI trimer was also predicted by Millard et aI., 10 based on matrix isolation analysis.…”