Transmission spectra of sublimed thin films of the α-crystalline forms of H2PC, CuPC, NiPC, CoPC, and ZnPC in the 0.5 to 0.9-μ region changed sharply as a result of α→β transformation induced by heat treatment above 300°C. The VOPC was unaffected. In the β-crystalline forms the absorption maxima (cm−1) were: H2PC 13 970, 15 500; CuPC 13 800, 15 540; NiPC 14 430, 15 900; CoPC 14 120, 15 730; and ZnPC 13 340, 15 430. The positions and contours of these bonds were to be expected on the basis of polarized single-crystal results reported by Lyons, Walsh, and White and Fielding and MacKay. Digital computer calculations of Davydov splittings for finite-sized “block”- and “bar”-shaped crystallites of CuPC based upon pairwise dipole–dipole interactions compared well with earlier results for the infinite sphere model in H2PC. Assignments for the four observed exciton components in β-H2PC must not only correctly predict the band positions and relative intensities, but should also be in accord with a red shift of each of the B2u and B3u vapor components. In the β crystal of the metal complex an intramolecular distortion or site symmetry should split the Eg molecular states. These in turn should also be red shifted and split by the crystal environment. The results, including studies of mixtures of several phthalocyanines in CuPC, are consistent with the interpretation.
The infrared spectrum between 4000 and 200 cm-1 of polycrystalline D202 at -190°C corresponds to that of H202 indicating that the crystal structure and spiral chain coupling of excitons for each of the six normal modes are the same in D 2 0 2 as in H 20 2. At temperatures near -100°C the crystal spectra of both H 2 02 and D20 2 change with time on CsI and CsBr cold windows. The greate ,t change observed is that the crystal bands arising from torsion disappear and are replaced by two other bands about 100 cm-1 lower in frequency. Also, the exciton bands in the stretching and bending regions lose their fine structure and shift to lower frequency indicating that the peroxides actually dissolve into the salt windows without decomposition at these low temperatures. The spectra of H20, and D20 2 matrix isolated in argon and nitrogen at about gOK are also reported. The most interesting features of these spectra are the extraordinarily broad bands in the torsional region, P4, in both nitrogen and argon. The relative intensities of the triplet in argon are observed to change reversibly with temperature. In argon matrices, spectra of the torsional region indicate that the motion of the peroxide in the cavity is similar to that in the gas phase. The techniques of earlier workers for analysis of hindered internal rotation were applied to calculate energy levels for the matrix-isolated molecule. In argon the triplet in the torsion band is explained in terms of combination sum and difference bands of the internal rotation with translational or librational modes. In a nitrogen matrix, the spectra indicate that the internal rotation is much more hindered. The breadth of the band is explained in terms of a coupling between the hindered internal rotation and translation and/or librational motion as well as combination sum and difference bands with these motions.
Infrared spectra of pyridine-H. and pyridine-D. in the solid state were measured between 4000 and 200 em-I. Frequencies and polarization of fundamental absorptions were established for oriented thin films of freshly crystallized samples. Behavior of the bands in polarized light aided in clarifying several assignments. The multiplicity of several of the bands was accounted for by close-lying overtones and combinations. Some of the components of V.6 are due to the existence of appreciable amounts of 13C isotope species clearly observable in a nitrogen matrix at 5°K. For pyridine-D. a phase transition was clearly observable after several hours of annealing of thin films at about -60°C, but similar transformation could not be induced in normal pyridine. The infrared crystal data are consistent with an orthorombic factor group established by x-ray analysis with no molecule on any symmetry element of the crystal. Raman spectra of liquid and solid pyridines are also reported.
The infrared spectrum of carbonyl sulfide has been examined as a polycrystalline film at 80°K and also in matrix-isolated form, using argon, nitrogen, and CS2 as the matrix materials. Particular attention has been given to the ν3 vibration, which appears as an abnormally broad and asymmetric band in solid OCS. The asymmetry of ν3 does not appear to be the result of any significant reflection effects nor is it due to disorder in the crystal. A study of the concentration dependence of the ν3 frequency in isotopic mixtures shows that a good part of the asymmetry can be attributed to the ν3 absorption of molecules containing 33S and 34S. Spectra of dilute mixtures of OCS in argon matrices display absorption by both isolated molecules and molecular pairs. The features of the spectrum are qualitatively accounted for in terms of a simple model of pairs interacting through transition-dipole coupling. In both N2 and CS2 matrices, the evidence suggests two different sites for the OCS molecule in the host lattice.
The infrared spectra of protonated and deuterated nitromethane isolated in a nitrogen matrix have been recorded from 4000 to 250 cm−1. Peaks have been assigned to monomer and dimer species by varying the concentration of nitromethane in the matrix. The frequencies of the monomer have been used in a normal coordinate analysis and the force constants evaluated agree well with those of the gas phase. The Cartesian displacements of the atoms for each normal mode are reported. These displacements showed that for the ``NO2 antisymmetric vibration'' there was considerably more motion of the hydrogen atoms. Lennard-Jones-type potentials were used to calculate dimer configurations with a minimum intermolecular potential energy, taking into account both dispersion and electrostatic forces. The charges on the atoms needed for the calculation of electrostatic forces were calculated from molecular orbital theory using both the MWH method and the INDO method. The position of minimum potential energy is a function of distance between a pair of nitromethane molecules and the angular rotation of two molecules with respect to each other. With the configuration of minimum potential energy and the Cartesian displacements in hand, the shifts and splittings due to intermolecular coupling could be evaluated by applying two-site, molecular exciton theory. The calculated shifts and splittings agree well with those observed in the spectra giving credibility to our calculations. The results will make it possible to estimate the moments of inertia of the dimer and force constants for the pair necessary for assessing partition functions for dimer formation under all conditions of temperature and pressure.
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