Phase shift cavity ring down at low temperatures: Vibration–rotation overtone absorption of H–D (Δv = 4) at 297 and 105 K

Phase shift cavity ring down (PS-CRD) spectroscopy has been used for the detection of a vibrational–rotational overtone transition (v = 0 → 4) of H–D at 297 and 105 K. The PS-CRD technique at low temperatures involves an optical cavity attached to a cryostat where the static cell and mirrors of the optical cavity are all at the same temperature. A novel design allows the alignment of the mirrors of the optical cavity at low temperatures without disrupting the vacuum in the chamber surrounding the cell. The peak absorption lines were corrected for distortion because the bandwidth (fwhm) of the laser in our experiment exceeds the width of the absorption lines. The calculated line strengths of the rotational transitions are in good agreement with literature values.