Free-jet studies of the visible spectroscopy of some perhalonitrosomethanes

Recent work on the electronic spectroscopy of halogen substituted nitrosomethanes in the visible spectral region is reviewed with particular reference to laser-induced fluorescence and photofragment yield spectra in supersonic free-jet expansions. The A(n, p*)-X electronic spectra in the 650-720 nm region are dominated by progressions in low frequency torsional modes, that reflect eclipsed to staggered dihedral conformational changes upon electronic excitation. The observed torsional progressions can be understood well on the basis of spectral simulations that utilize a simple one-dimensional Hamiltonian for the hindered internal rotation. The relevance of these laser spectroscopic studies for current work on the state-selected photophysics and photodissociation dynamics of the title compounds is highlighted. © 1990.