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- W160624352 abstract "The photodissociation dynamics of trans-methyl nitrite and atmospherically relevant alkyl ketones in the near UV were studied by velocity map imaging.The photolysis of trans-methyl nitrite excited to the S1 state with 0 and 1 quanta of excitation in the N=O-stretching mode, has been investigated. The primarily NO fragments were probed by (1+1) REMPI. The results demonstrate two dissociation pathways: a vibrationally non-adiabatic predissociation, and an adiabatic channel via tunneling through a potential barrier on the S1 potential energy surface. The O-NO bond dissociation energy was determined to be D = 38.8 kcal/mol and an S1 excited state lifetime of t = 350 fs was found. The photodissociation dynamics of acetone-h6 excited within the first absorption band (340 - 230 nm) was investigated by detecting the nascent CH3 fragments in their ground state by (2+1) REMPI. The dissociation of acetone to CH3 and CH3CO fragments is not direct and proceeds via three pathways corresponding to three spectral regions of the excitationwavelengths. In region 1 (333.5 - 305.3 nm), acetone is excited to the S1 state followed by internal conversion to the S0 state with unimolecular decay on it. Acetone excited in region 2 (305.3 - 260 nm) dissociates over a smallbarrier on the T1 surface (“tight” transition state). The height of the barrier was measured to be 13.4 kcal/mol. In region 3 ( < 260 nm), secondary dissociation of CH3CO to CH3 and CO was observed. The C-C bond dissociation energywas measured to be D = 83.2 kcal/mol. The same experiments were carried out on acetone-d6 by probing the CD3 fragments.Isotopic substitution did neither demonstrate any noticable effect on the photodissociation dynamics nor on the C-C bond dissociation energy. This was interpreted as that the deuteration decreases the zero-point energy of acetone in theT1 state and in the transition state. The rotational energy of the molecule itself and its internal rotors might lower the effective T1 barrier height. The dissociation limitof acetyl-d3 was affected by the deuteration. The dissociation limit of acetyl-d3 was estimated to be 19.5 kcal/mol, that in acetyl-h3 is known to be 17 kcal/mol. Theincrease upon deuteration may partially reflect the longer lifetime of the acetyl-d3 radical toward unimolecular dissociation.The photolysis of methyl ethyl ketone via (a) CH3C(O)C2H5 + hv = CH3 + C2H5CO and (b) CH3C(O)C2H5 + hv = C2H5 + CH3CO channels was studied by probing CH3 via (2+1) REMPI for reaction (a), and C2H5 by (1+1) REMPI for reaction (b). The ion distribution was found to be independent of excitation energy. The present results do not provide enough datafor a quantitative analysis. Further experimental and theoretical investigations would be of great interest." @default.
- W160624352 created "2016-06-24" @default.
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- W160624352 date "2008-11-25" @default.
- W160624352 modified "2023-09-23" @default.
- W160624352 title "Photodissociation dynamics of atmospherically relevant alkyl ketones and methyl nitrite by velocity map imaging" @default.
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