Spectroscopy and non-equilibrium distribution of vibrationally excited methane in a supersonic jet

High-resolution spectra of supersonic jets of vibrationally excited methane have been recorded by diode laser in the 8 mu m region. A formalism for the description of energy distribution is proposed. It allows to estimate populations of vibrational polyads. Under these non-equilibrium conditions, translational temperature is also measured from line profiles. For relaxation, it is shown that vibrational relaxation between polyads is negligible whereas strong redistribution of population arises inside each polyad. Spectroscopically, observed lines involving the first four excited polyads allows cross-checked tests for energy level analysis. (C) 1998 Elsevier Science Ltd. All rights reserved.