STIMULATED RAMAN SPECTROSCOPY OF SOLID PARAHYDROGEN

$^{1.}$ T. Momose, D.P. Weliky, and T. Oka, J. Mol. Spectrosc. 153, 760 (1992).Author Institution: Department of Chemistry and Department of Astronomy and Astrophysics, The University of ChicagoThe stimulated Raman spectra of the $Q_{1}(0) (v=1 \leftarrow 0, J=0 \leftarrow 0)$ and the $Q_{1}(1) (v=1 \leftarrow 0, J=1 \leftarrow 1)$ transition of a solid parahydrogen crystal has been studied using high resolution stimulated Raman gain spectroscopy with CW lasers. At a low $J=1$ hydrogen concentration (0.06\%), the $Q_{1}(0)$ transition showed a sharp single line ($HWHM=15MHz$) with no hint of asymmetry or satellites as reported $previously.^{(1)}$ By increasing the $J=1$ hydrogen concentration (0.2\%), the spectrum became broader ($HWHM=30MHz$) and showed some weak structure at lower infrared frequency. The width of the weak feature was approximately 750MHz. The broadened transition observed at higher $J=1$ hydrogen concentration shows a breakdown of the excition momentum selection rule $\Delta k=0$ due to the scattering of $v=1$ Bloch waves by J=1 impurity molecules. The mechanism for the appearance of the weak feature has not been undestood. The $Q_{1}(1)$ Raman transition of a parahydrogen crystal with 0.2\% $J=1$ hydrogen, which was two orders of magnitude weaker than the $Q_{1}(0)$ transition, was a sharp line ($HWHM \sim 70MHz$) with weak structures at lower frequency. The sharpness of this transition is due to the localization of the exciton, whereas that of the $Q_{1}(0)$ Raman transition is due to $\Delta k=0$ selection rules