Wenge, Andreas M. and Schmaunz, Andreas and Kensy, Uwe and Dick, Bernhard (2012) Photodissociation dynamics of tert-butylnitrite following excitation to the S-1 and S-2 states. A study by velocity-map ion-imaging and 3D-REMPI spectroscopy. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 14 (19). pp. 7076-7089. ISSN 1463-9076,
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Excitation of tert-butylnitrite into the first and second UV absorption bands leads to efficient dissociation into the fragment radicals NO and tert-butoxy in their electronic ground states (2)Pi and E-2, respectively. Velocity distributions and angular anisotropies for the NO fragment in several hundred rotational and vibrational quantum states were obtained by velocity-map imaging and the recently developed 3D-REMPI method. Excitation into the well resolved vibronic progression bands (k = 0, 1, 2) of the NO stretch mode in the S-1 <- S-0 transition produces NO fragments mostly in the vibrational state with v = k, with smaller fractions in v = k - 1 and v = k - 2. It is concluded that dissociation occurs on the purely repulsive PES of S-1 without barrier. All velocity distributions from photolysis via the S-1(n pi*) state are monomodal and show high negative anisotropy (beta approximate to -1). The rotational distributions peak near j = 30.5 irrespective of the vibronic state S-1(k) excited and the vibrational state v of the NO fragment. On average 46% of the excess energy is converted to kinetic energy, 23% and 31% remain as internal energy in the NO fragment and the t-BuO radical, respectively. Photolysis via excitation into the S-2 <- S-0 transition at 227 nm yields NO fragments with about equal populations in v = 0 and v = 1. The rotational distributions have a single maximum near j = 59.5. The velocity distributions are monomodal with positive anisotropy beta approximate to 0.8. The average fractions of the excess energy distributed into translation, internal energy of NO, and internal energy of t-BuO are 39%, 23%, and 38%, respectively. In all cases similar to 8500 cm(-1) of energy remain in the internal degrees of freedom of the t-BuO fragment. This is mostly assigned to rotational energy. An ab initio calculation of the dynamic reaction path shows that not only the NO fragment but also the t-BuO fragment gain large angular momentum during dissociation on the purely repulsive potential energy surface of S-2.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | JET-COOLED METHYL; T-BUTYL NITRITE; MOLECULAR-BEAM; ALKYL NITRITES; NO FRAGMENT; ENERGY-DISTRIBUTION; SUPERSONIC JET; INVERSION; CH3ONO; NM; |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie > Chair of Chemistry III - Physical Chemistry (Molecular Spectroscopy and Photochemistry) > Prof. Dr. Bernhard Dick |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 25 May 2020 08:37 |
| Last Modified: | 25 May 2020 08:37 |
| URI: | https://pred.uni-regensburg.de/id/eprint/19502 |
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