High-resolution Fourier-transform spectroscopy of solid parahydrogen in the first overtone region

Abstract

The first vibrational overtone spectrum of solid parahydrogen with various low orthohydrogen impurity levels has been studied in the range 7900--10 000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ using a White-type external multireflection system with a 34.8-cm sample path length. We were able to detect extremely weak features, namely, the ${\mathrm{Y}}_{1}$(0) at 7991.85 (1) ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, and the double transitions ${\mathrm{U}}_{1}$(0) + ${\mathrm{Q}}_{1}$(1), ${\mathrm{U}}_{1}$(0) + ${\mathrm{S}}_{1}$(0), ${\mathrm{U}}_{1}$(1) + ${\mathrm{Q}}_{1}$(0), and ${\mathrm{Q}}_{1}$(0) + ${\mathrm{Q}}_{1}$(0). The ${\mathrm{Q}}_{1}$(0) + ${\mathrm{Q}}_{1}$(1) and ${\mathrm{Q}}_{1}$(1) + ${\mathrm{Q}}_{1}$(1) double transitions were resolved. We obtained a rich orthohydrogen satellite spectrum associated with the transitions ${\mathrm{Q}}_{2}$(0) and ${\mathrm{Q}}_{2}$(1) near 8060 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. An analysis and assignment of these satellite transitions are presented. The double transitions of the type ${\mathrm{Q}}_{1}$(J) + ${\mathrm{Q}}_{1}$(${\mathrm{J}}^{|\mathrm{I}\mathrm{H}}$) (J,${\mathrm{J}}^{|\mathrm{I}\mathrm{H}}$ = 0,1) are located in the spectral region around 8300 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The most remarkable features here are the ${\mathrm{Q}}_{1}$(1) + ${\mathrm{Q}}_{1}$(1) transition, which consists entirely of fine structure, and the ${\mathrm{Q}}_{1}$(0) + ${\mathrm{Q}}_{1}$(0) transition, which, to our knowledge, has an intensity that cannot be accounted for by previously proposed mechanisms. Finally the thermal shift of all of the above-mentioned transitions was investigated by lowering the sample temperature from 12.5 K down to 6.5 K while taking spectra. The influence of the change of temperature on the line positions, linewidths, and interaction parameters of solid hydrogen is discussed.