Photodissociation Dynamics of no Containing Molecules.
Abstract
Predissociation processes of NCNO and t-BuNO following laser excitation have been investigated in detail. In the case of NCNO, excited-state lifetime measurements for the parent molecule confirm that NCNO belongs to the small molecule limit when excited below the dissociation threshold. Experimental results for the nascent NO fragment show that rotational excitation can be modeled by phase space theory (PST), but vibrational state populations are larger than PST prediction. The separate statistical ensembles (SSE) model, by Wittig and co-workers, can predict correctly the vibrational excitation. The NO spin-orbit state population is 'cold' relative to the V, R degress of freedom. The high J states of NO show a preference in the Pi(A ^') component of the Lambda -doublet levels, and this is in line with dissociation on the ground surface of NCNO (i.e. S_0 (A^')). Product state correlations and spatial anisotropies were investigated via CN sub-Doppler spectroscopy. The correlations further prove that the dissociation is statistical, and the observed vibrational excitation can be fit closely by the SSE model than PST. The spatial anisotropy is less than the experimental sensitivity, which is in line with the statistical behavior of the dissociation process. In the case of t-BuNO, two dissociation channels are identified as singlet and triplet surfaces. Spectroscopy of the parent molecule on the S_1 surface allowed internal rotation to be explored. For the singlet surface dissociation, we observe two main phenomena. First of all, the lifetime of the initially prepared excited state is short, but the dissociation time is long. This can be explained by the large density of states on the ground-state surface. Secondly, the NO state distributions are statistical, suggestive of dissociation without a barrier. However, for triplet surface dissociation, the dissociation time is fast and the NO product state distribution is non-statistical, i.e., the rotational excitation is lower than the prior prediction. The spin-orbit population is also lower than what is yielded by the prior simulation. A small barrier for the triplet surface dissociation has been postulated, and the existence of such a barrier agrees with the experimental observations and theoretical calculations for similar molecules. (Copies available exclusively from Micrographics Department, Doheny Library, USC, Los Angeles, CA 90089-0182.).
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1988
- Bibcode:
- 1988PhDT.........1Q
- Keywords:
-
- Physics: Molecular