Infrared spectrum of hydrogen in the condensed phase with high-sensitivity spectrometers: Experiments with a 0.04-cm−1 Fourier transform spectrometer in the range 1.5–12 μm

The infrared spectrum of solid and liquid hydrogen was recorded using a Fourier spectrometer. The pure rotational U transitions, U₀(0) in solid para hydrogen and U₀(1) in solid normal hydrogen, with the accompanying phonon branches were observed for the first time. In addition, the rotational double transitions S₀(0) + S₀(1) and S₀(1) + S₀(1) were identified. The identifications of these transitions are based on positions calculated by making use of gas phase molecular constants. In the liquid the double transitions are preserved but the single transitions U₀(0) and U₀(1) are entirely absent. The region of Q_1←0(J) reveals structure which has not been reported before. Its interpretation is presented.