METHANE-NV1(A1) VIBRATIONAL-STATE ROTATIONAL STRUCTURE OBTAINED FROM HIGH-RESOLUTION CARS-SPECTRA OF THE Q-BRANCH

The gaseous methane ν1(a1), Q-branch coherent anti-Stokes Raman scattering (CARS) spectra have been investigated at a resolution of 0.002 cm-1. A complex rotational structure of the resolved Q-branch has been experimentally observed. This structure can be ascribed to strong tetrahedral splitting of the rotational levels of the upper vibrational state, which possibly occurs due to Fermi resonance between the ν1(a1) and 2ν2(a1) vibrational energy levels which are close to each other. An assignment of the observed spectral lines has been made, yielding the rotational constants B, D, and Dt for the ν1(a1) vibrational state of the methane molecule. The absolute Raman frequency ν1 of the purely vibrational transition has been found. © 1979.