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.

Infra-red spectra are reported of binary mixtures of HCI, HBr or HI (HX) with O,, N2, COz, CO or CzH4 (D) in argon matrices at 20 K. With the exception of Oz. three induced absorption bands are observed which are interpreted as arising from HX-D, HX-D-HX and (HX),-D interactions.

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.

Infra-red spectra are reported of the halogenomethanes and the C2 to C4 iodoalkanes isolated in argon matrices at 20K. The observed bands are correlated with the different conformers of the iodopropanes and iodobutanes. Concentration studies of the halogenomethanes in argon matrices show the growth of multimer bands, the predominant species being a linear dimer. The spectrum of solid fluoromethane is also reported. No evidence was found for rotation of fluoromethane in either argon or methane matrices. * iiquid phase frequemy, ref. (23).

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