Dolphus E. Milligan

Infrared Spectroscopic Evidence for the Rotation of the Water Molecule in Solid Argon

High‐resolution spectra of H2O, HDO, and D2O suspended in solid Ar have been observed in the range 4°—27°K. Evidence has been obtained for the rotation of these species in Ar matrices. The majority of the observed lines are found to be in very good agreement with low‐J transitions of the gas spectra, allowing for a small matrix shift. Transitions arising from both spin modifications of H2O and D2O have been observed and the observed intensities suggest that a large degree of spin equilibration has taken place. A small contamination of O2 may be responsible for this. A perturbation of one of the rotational levels of ν2—H2O is discussed.

Infrared Spectroscopic Study of the Photolysis of Methyl Azide and Methyl‐d3 Azide in Solid Argon and Carbon Dioxide

Experiments have been carried out on the photolysis of methyl azide and methyl‐d3 azide at high dilution in solid argon (4.2°K) and carbon dioxide (∼50°K). Photolysis of these species in argon and carbon dioxide matrices results in the appearance of a number of new spectral features in the 3300–600 cm—1 region. The spectroscopic data for the photolysis products appear to be consistent with the identification of these species as methyleneimine (CH2=NH) and methyleneimine‐d3 (CD2=ND).

Infrared Spectroscopic Evidence for the Species HNC

Infrared absorptions observed following the photolysis of mixtures of HI and O2 in an Ar matrix at 4°K appear to be contributed by HO2 produced in the matrix. Studies on isotopically substituted systems support this assignment. The two oxygen atoms have been shown to be nonequivalent. Approximate force constants and thermodynamic functions for HO2 are tabulated.

Molecular Rotation and Ortho—Para Nuclear Spin Conversion of Water Suspended in Solid Ar, Kr, and Xe

Additional data supporting the nearly free rotation of the water molecule trapped in a rare‐gas lattice are presented. Ortho—para spin conversion is strongly induced by adding O2 to the matrix. A simple model is suggested which correlates the intensities observed for H2O, HDO, and D2O suspended in Ar, and which estimates the rate of nuclear spin conversion to within a factor of 5 or 10. The majority of the water molecules occupy substitutional sites in the lattice obtained by removing a single rare‐gas atom.Several sharp, intense lines are tentatively assigned to the H bonded OD stretch of HDO and D2O dimers in Ar. They contrast markedly with the corresponding broad band of the OH stretch.

Matrix‐Isolation Study of the Vacuum–Ultraviolet Photolysis of Dischlorosilane. The Infrared Spectrum of the Free Radical SiCl2

In studies of the vacuum–ultraviolet photolysis of SiH2Cl2 and of SiD2Cl2 suspended in an argon matrix at 14°K, new absorptions appear at 502 and at 513 cm−1 which may be assigned as the two stretching fundamentals of SiCl2. A broad, unstructured absorption is also observed in the region of the ultraviolet spectrum in which features tentatively ascribed to SiCl2 were observed in earlier gas‐phase emission studies. The detailed assignment of the observed infrared features is considered, and values of the valence angle, the Si–Cl stretching force constant, and the stretching–interaction force constant are estimated, corresponding to the two possible assignments for the infrared absorptions.

Infrared Spectroscopic Evidence for the Rotation of the Ammonia Molecule in Solid Argon and Nitrogen

High‐resolution infrared spectra (of the symmetric bending mode) of ammonia suspended at high dilution in solid argon and nitrogen have been obtained. More than a half dozen extremely sharp bands have been observed in the 950–1040 cm—1 region (in the spectrum of ammonia) in these materials under conditions where there should be little if any absorption due to polymeric species. The frequency separations of the bands, their temperature dependence, and their extreme sharpness appear to be compatible with a model in which the ammonia molecule executes quantized rotation in these solids.

Matrix‐Isolation Study of the Vacuum‐Ultraviolet Photolysis of Chlorofluoromethane. The Infrared and Ultraviolet Spectra of the Free Radical ClCF

The vacuum‐ultraviolet photolysis of CH2ClF and of CD2ClF isolated in an argon matrix at 14°K leads to the appearance of prominent absorptions at 742 and at 1146 cm−1 which have been assigned to the two stretching fundamentals of ClCF. A weak absorption band system between 3900 and 3400 A, with a 376 ± 10 cm−1 average band spacing, may be tentatively attributed to ClCF, as may be an emission band system which appears between 4000 and 4900 A when the sample is excited by 3650‐A radiation. The 379 ± 10 cm−1 average band spacing associated with this emission band system has been tentatively attributed to the bending mode of ground‐state ClCF, permitting a normal coordinate analysis for this molecule. The bending and the C–Cl stretching modes are appreciably mixed. Several other groups of absorptions also have been observed in these experiments, but the species responsible for them have not been definitively identified.

The infrared spectra of thick films of CO2 and CO2 + H2O at low temperatures

Abstract High-resolution infrared-absorption studies on thick films of CO 2 and on dilute solid solutions of H 2 O in CO 2 have been made at 53°K and at 4δK. A spectroscopically observable complex between CO 2 and H 2 O is not formed. The isolation of H 2 O in the CO 2 matrix at 53°K is quite good. Monomer and dimer absorptions have been assigned in the 1600–1650 cm −1 region. In very thick films of pure CO 2 ν 1 appears, weakly, at 53°K. In samples deposited at 4°K the ν 1 absorption is markedly intensified, probably because of an increased number of crystal imperfections, and 2ν 2 is also observed. Similar systems of lattice vibrations have been observed in combination with both ν 2 and ν 2 .

Infrared Spectroscopic Study of the Photolysis of HN3 in Solid CO2

Infrared studies have been carried out on the photolysis of HN3 and DN3 in CO2 matrices at 20° and 53°K. HNO and DNO have been identified as products of the reaction of NH and ND with CO2. The presence of HNO has been confirmed by the detection of absorptions at 7400, 7100, and 6850 A in the visible spectral region. Evidence has also been obtained for the production of a 1:1 compound between NH (ND) and CO2. Several possible structures for this species are discussed.

Infrared Study of the Reaction of CH2 with CO2 in the Solid State

The photolysis of CH2N2 and of CD2N2 in CO2 at temperatures near 50°K has been studied using infrared techniques. Evidence has been obtained for the production of one or more intermediates by the reaction of CH2 with CO2. These intermediates are precursors of H2CO+CO. Possible structures for such species are proposed and discussed.