Knowledge Bank

Laser excitation of the $NO2A¯2B2/B¯2B1$ states at $20,000-22,000cm-1$ yields highly vibrationally excited $X-2A1NO2$ because of strong vibronic coupling between the $A¯2B2/B¯2B1$ and $X¯2A1$ states. The highly vibrationally excited $X¯-2A1NO2$ is subsequently deactivated by collisions with the bath gas. The progress of vibrational relaxation was followed through the time (500 ns) and frequency ($\ge 1cm-1$) resolved NIR/IR emission recorded by time-resolved Fourier transform emission spectroscopy. In addition, IR emission was observed from excited vibrational levels of the bath gas which were populated by vibrational energy transfer from the hot $NO2$ molecules. The nature of the high vibrational levels of $NO2$ at $22,000-20,000cm-1$ and their relaxation will be discussed.