Design of a low temperature phase shift cavity ring down technique with applications to high vibrational overtone absorptions

A phase shift cavity ring down (PS-CRD) low temperature technique is presented. The technique combines a phase shift cavity ring down optical cavity within a cryogenic vacuum chamber for thermal isolation. The long optical pathlengths provided by PS-CRD allow for direct absorption measurements of high vibrational overtones to be observed. Phase shift cavity ring down (PS-CRD) spectroscopy of high vibrational overtones of (v = 0 → 5) ethylene, methane, ethane, and propane were obtained and compared with Fourier Transform visible spectroscopy (FT-Vis) at 298K. The C-H stretching (v = 0 → 6) overtones of ethene, ethane, propane, butane, pentane at 298K are presented. High vibrational overtones of deuterated methanes CH₄, CH₃D, CH ₂D₂, CHD₃ at room temperature and at low temperatures are reported. The rotationally resolved C-H overtone of (v = 0 → 5) CHD ₃ at temperatures 298K, 176K, and 102K are shown. The (v = 0 → 4 and v = 0 → 5) transitions of HD are presented at room temperature. The (v = 0 → 4) transition is shown at measured temperatures of 298K and 156K. A temperature calculation is also presented.