Diagnostics of vibrational excitation of ethanol molecules by the infrared fluorescence method

An experimental investigation was carried out of the dynamics of vibrational multiphoton excitation of molecular ethanol by a CO₂ laser pulse. Energy transfer from a resonant laser-excited vibrational mode to a nonresonant mode was studied. The energy of the nonresonant mode was measured by recording the infrared fluorescence with nanosecond time resolution. In a wide energy range the intensity of the spontaneous infrared fluorescence is found experimentally to be proportional to the number of photons in the corresponding vibrational mode of a gas of polyatomic molecules. A simple expression is given for the dependence of the average energy in the mode on the total energy of the equilibrium gas. It is shown that the distribution function during the multiphoton excitation process is of a nonequilibrium nature. The lower limit of stochastization of the vibrations in the ethanol molecule is estimated.