Vibrational relaxation of highly excited NCNO in collisions with He, Ar and N-2

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 S-1 state whence radiationless transitions transfer the molecules to high vibrational levels of the S-0 ground state below the dissociation lim it. IRF was observed at ca. 4.6 mum, corresponding to fundamentals in the C N stretching vibration of NCNO. Values of << DeltaE >>, the mean energy rem oved per collision with the diluent gas (Ar, N-2 or He) were derived as a f unction of << E >>, the mean internal energy content of the excited molecul es. The variation of << DeltaE >> with << E >> was approximately linear and , at << E >> = 10 000 cm(-1), << DeltaE >> = 0.44 +/- 0.03 cm(-1) for Ar, < < DeltaE >> = 0.62 +/- 0.04 cm(-1) for N-2 and << DeltaE >> = 0.57 +/- 0.04 cm(-1) for He.