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

The first vibrational overtone spectrum of solid parahydrogen with various low orthohydrogen impurity levels has been studied in the range 7900--10 000 cm^-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 Y₁(0) at 7991.85 (1) cm^-1, and the double transitions U₁(0) + Q₁(1), U₁(0) + S₁(0), U₁(1) + Q₁(0), and Q₁(0) + Q₁(0). The Q₁(0) + Q₁(1) and Q₁(1) + Q₁(1) double transitions were resolved. We obtained a rich orthohydrogen satellite spectrum associated with the transitions Q₂(0) and Q₂(1) near 8060 cm^-1. An analysis and assignment of these satellite transitions are presented. The double transitions of the type Q₁(J) + Q₁(J|IH) (J,J|IH = 0,1) are located in the spectral region around 8300 cm^-1. The most remarkable features here are the Q₁(1) + Q₁(1) transition, which consists entirely of fine structure, and the Q₁(0) + Q₁(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.