The Raman spectrum of an oriented single crystal of CaSO4∙2H2O has been recorded from 20 to 3600 cm−1 at 300 °K and 77 °K using polarized laser excitation. The symmetries of the observed Raman lines have been determined and the spectrum has been analyzed in terms of external lattice vibrations, internal vibrations of the SO4 and H2O groups, hydrogen bond vibrations, and combinations of these vibrations. The translatory and rotatory lattice modes of the H2O molecules have been identified and the latter have been correlated with the principal moments of inertia of the water molecule. The hydrogen bond vibration was observed at 210 cm−1 at 300 °K and 217 cm−1 at 77 °K. The assignments of the internal modes were found to be consistent with the results of previous workers. Several overtone and combination frequencies were observed, especially in the region of the ν1 and ν3 vibrations of H2O.

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The first-order Raman spectra of CdF2 and PbF2 have been recorded at 300, 77, and 4.2 °K. The spectrum in each case is a single line, arising from the triply degenerate F2g lattice mode. The observed frequency of this mode is 315 cm−1 in CdF2 and 257 cm−1 in PbF2. The frequencies shift slightly and the lines narrow considerably when the crystals are cooled. The Raman frequencies are used, together with previously known infrared and elastic data, to calculate the parameters of the rigid ion and the dipole shell models for these crystals.

The frequencies and shapes of the vibrational Raman lines, Ql(0) and Q l ( l ) , of solid hydrogen a t 2.1 'I< have been studied for a series of ortho-para rat~os, c,/c,. In the concentration range 0.75 > c, > 0.20 and 1.0 > c, > 0.25, each Q line has a single maximum, and can be interpreted in terms of traveling vibrational excitations. For c0 < 0.20 the Q l ( l ) line splits into a band of closely spaced lines; a t these low concentrations traveling ortho excitat~ons apparently cannot be sustained, and the components of the Ql(1) line represent various nearestneighbor couplings of ortho molecules. Some observations on the Sl(0) line were also made. IKTRODUCTIONIn a n earlier investigation of the Raman spectrum of solid hydrogen (Bhatnagar et al. 1962) it was found that the frequency and half-width of the parahydrogen line, Ql(0) (v" = 0, Av = 1 ; J" = 0, AJ = 0), were not the same in normal hydrogen and in parahydrogen. The corresponding orthohydrogen line, Ql(1) (v" = 0, Av = 1 ; J" = 1 , AJ = 0), naturally did not appear in the spectrum of pure parahydrogen, but in the spectrum of normal hydrogen its frequency -\\as shifted further from the value for the low-density gas (Stoicheff 1957) than was that of Ql(0). I t was concluded that, if the changes in the frequencies and contours of these lines were followed through a series of samples of different ortho-para ratios, information concerning interactions involving ortho nlolecules could be obtained. The experiments described below were therefore undertaken. T h e Ql(0) and Q1(l) lines were studied in mixtures containing 25% t o 100% parahydrogen and the parahydrogen rotationvibrational line, Sl(0) (v" = 0 , Av = 1 ; J" = 0, AJ = 2), was studied in mixtures containing 70% to 100% parahydrogen. EXPERIMENTAL

Raman scattering from single crystals of potassium acidphthalate has been observed with the 4880 di and 5145 di excitations of an argon ion laser. The room temperature Raman spectra, recorded with a Jarrel-Ash spectrometer, in the region 0-300 cm-', exhibit broad bands which are attributed to the translatory and rotatory types of lattice vibrations of the potassium and acid phthalate ions in the crystal. Experiments were carried out at 77 K using a Spex double monochromator and the Raman scattering in the second-order of the gratings were observed. The result was a splitting of the several broad bands into their components. Assignments of these low frequency Raman spectra, consistent with the crystal structure and the group theoretical predictions is given. Variations in intensities of some of the spectra due to crystal orientation are also observed and briefly discussed.