Knowledge Bank

The high resolution Raman spectrum of the vibration-rotation transition $Q1\leftarrow 0(0)(v=1\leftarrow 0,J=0\leftarrow 0)$ of solid parahydrogen has been studied using stimulated Raman gain spectroscopy with tone burst $modulation.(1)$ The observed spectrum shows a sharp single line with the linewidth of -7MHz (HWHM). The measured frequency of $4149.75cm-1$ is in good agreement with $4149.81cm-1$ reported $earlier.(2)$ The observed single line has no hint of asymmetry or satellites. We have searched $2.5cm-1$ above and below the observed line and found on other spectral features, which suggests that our crystal is purely hexagonal close packed(hep). The sharpness of the observed line is not due to the localization of exciton as in the most of our infrared spectral lines, but it is due to the exciton momentum selection rule $\Delta k=0(3)$. The present observations demonstrates the purity of the quantum state of the hydrogen molecules in the solid.