Nuclear Spin Symmetry Conservation Studied for Symmetric Top Molecules (CH3D, CHD3, CH3F, and CH3Cl) in Supersonic Jet Expansions

We report results on nuclear spin symmetry conservation studied by high resolution spectroscopy of relative line intensities for the A and E nuclear spin isomers of symmetric top molecules CHD3, CH3D, CH3F, and CH335Cl in supersonic jet expansions with He and Ar as carrier gases. Infrared absorption spectra were measured around 3000 cm-1 by an infrared (lead salt) diode laser and a continuous wave IR-OPO (infrared optical parametric oscillator) locked to a frequency comb. A detailed analysis of the R(2)-line intensities of the CH-stretching fundamental shows that nuclear spin symmetry is conserved for CHD3, CH3F, and CH335Cl during the expansion. For CH3D, a small contribution from nuclear spin symmetry relaxation cannot be excluded completely under our experimental conditions.