Investigation of the dissociation of CH3CN and CH3NO2 molecules in an infrared field by laser-induced fluorescence

An investigation was made of the dissociation of CH₃CN (excitation of the ν₄ and ν₇ vibration modes) and CH₃NO₂ molecules (excitation of the ν₇ vibration mode) accompanied by the formation of CN(X²Σ⁺) radicals in the field of a high-power CO₂ laser pulse. An investigation of the formation kinetics of CN radicals by laser-induced fluorescence showed that CN(X²Σ⁺) are the primary dissociation products of the CH₃CN molecule. Collisionless dissociation of CH₃CN during the excitation of the ν₇ vibration mode is governed by the laser pulse power and not by its energy, the power threshold being 1.1–1.2 GW/cm². At subthreshold infrared field powers, CN(X²Σ⁺) radicals can be formed as a result of the collisional mechanism of overcoming the anharmonicity in the lower vibrational levels. Laserinduced fluorescence may be used successfully to determine the lifetimes of the CN radicals in the systems under study. Different mechanisms for molecular dissociation in an infrared field and their relationship with the molecular parameters are discussed.