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 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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The 5000–8000-Å transmission spectra of H2PC and CuPC embedded in an argon matrix at 5°K at molar ratios of 4000:1 are very similar to their spectra in liquid solution. The predominant CuPC species in the matrix are isolated molecules, but a strong sideband in more concentrated mixtures (1000 Ar:1 CuPC) is attributed to interacting pairs. Coupling of transition dipoles was invoked to correlate the observed spectrum with several CuPC “dimer” configurations. Computer calculations based upon nonbonded atom–atom potentials were conducted to find the most probable relative orientations of two neighboring solute CuPC molecules. H2PC does not appear to show the effects of pairs even in extremely dilute solutions. A strong doublet which is very similar to that in liquid solution persists in the matrix.

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