Abstract
S-Nitrosothiols serve as carriers and donors of NO in several important biological signaling systems. In these compounds the S-NO bond is rather labile and NO can be released thermally or photochemically. This paper reports on the photolytical decomposition of tert-butylthionitrite (t-BuSNO) in the visible and near-UV spectral regions. Between 500 and 605 nm several vibronic levels of the S-1 (n ...
Abstract
S-Nitrosothiols serve as carriers and donors of NO in several important biological signaling systems. In these compounds the S-NO bond is rather labile and NO can be released thermally or photochemically. This paper reports on the photolytical decomposition of tert-butylthionitrite (t-BuSNO) in the visible and near-UV spectral regions. Between 500 and 605 nm several vibronic levels of the S-1 (n pi*) state were excited, including the electronic origin. At 360 nm t-BuSNO is excited near the maximum of the first UV band assigned to the S-2 (pi pi*) state. The velocity distributions of several hundred rovibrational states of the NO fragments were recorded with the recently developed 3d-REMPI method. A global fit to these data yields populations of the rovibrational states in both spin-orbit components of the (2)Pi electronic state of NO as well as their velocity distributions and angular anisotropies beta. These data also carry the distribution functions for internal and kinetic energy of the counterfragment, the t-BuS radical. The range found for the anisotropy parameter confirms the n pi* character of the visible absorption band (-1.0 < beta < -0.8), and the pi pi* character of the UV band (beta = 1.2). Mode-specific dissociation has been observed for excitation into several vibronic bands of the S-0 -> S-1 transition. Some produce NO exclusively in the v = 0 vibrational ground state, whereas some others produce NO almost entirely in the v = 1 vibrationally excited state. It is concluded that photodissociation is faster than relaxation of the NO stretch vibration of t-BuSNO in S-1 and that it proceeds on purely repulse potential energy surfaces in both electronic states.
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