Vibrational relaxation of highly excited NCNO in collisions with He, Ar and N2

Abstract

The relaxation of vibrationally highly excited NCNO has been studied using the technique of time-resolved infrared fluorescence (TR-IRF). A pulsed dye laser operating at 600 nm, or in some experiments at 640 nm, excited NCNO to its S₁ state whence radiationless transitions transfer the molecules to high vibrational levels of the S₀ ground state below the dissociation limit. IRF was observed at ca. 4.6 μm, corresponding to fundamentals in the CN stretching vibration of NCNO. Values of ΔE , the mean energy removed per collision with the diluent gas (Ar, N₂ or He) were derived as a function of E , the mean internal energy content of the excited molecules. The variation of ΔE with E was approximately linear and, at E = 10000 cm⁻¹, ΔE = 0.44 ± 0.03 cm⁻¹ for Ar, ΔE = 0.62 ± 0.04 cm⁻¹ for N₂ and ΔE = 0.57 ± 0.04 cm⁻¹ for He.