Photodissociation of Acetic Acid in the Gas Phase:  An ab Initio Study

Abstract

Photodissociation of acetic acid in the gas phase was investigated using ab initio molecular orbital methods. The stationary structures on the ground-state potential energy surfaces were mainly optimized at the MP2 level of theory, while those on the excited-state surfaces were determined by complete active space SCF calculations with a correlation-consistent basis set of cc-pVDZ. The reaction pathways leading to different photoproducts are characterized on the basis of the computed potential energy surfaces and surface crossing points. The calculations reproduce the experimental results well and provide additional insight into the mechanism of the ultraviolet photodissociation of acetic acid and related compounds.

Photochemistry and Vibrational Spectroscopy of the Trans and Cis Conformers of Acetic Acid in Solid Ar

“…17 In that study, it has been shown that the transition state for C-C cleavage on the T 1 surface has a geometry very similar to that of cis-acetic acid, whereas the transition state for C-O cleavage on the T 1 surface and for both C-C and C-O cleavages on the S 1 surface are connected geometrically to trans-acetic acid. 17 This means that the branching ratio between radicals could in principle be affected by the molecular conformation. In practice, because T 1 r S 0 is a forbidden transition and at the S 1 /T 1 crossing point the T 1 Franck-Condon geometry is already relaxed to a geometry bearing no memory of the initially excited conformer, decomposition to radicals on the T 1 surface seems to be conformationally independent.…”

“…Methane is expected to be formed together with CO 2 , from recombination of the CH(D) 3 and OCOH(D) radicals formed after C-C bond cleavage on the T1 surface. 17 Nevertheless, the bands of methane are not readily identified after photolysis of CD 3 COOD (Table 3), which is most probably due to the much smaller IR absorption cross section of methane modes as compared with CO 2 . In the photolysis of CH 3 COOH we assigned one band emerging at 1308.3 cm -1 to methane reported previously at 1307.7 cm -1 .…”

Isomerization and electronic relaxation of azobenzene after being excited to higher electronic states

“…CASSCF calculation has been widely used to deal with the excited states relevant to photochemical and photophysical processes [38]. It can give accurate descriptions of the PESs in both the ground and excited states [39][40][41][42][43][44]. The optimization of the stable structures and transition states were performed at the state-specific CASSCF level.…”

Photodissociation of organic molecules in star-forming regions

“…Its underlying decomposition dynamics (dissociation pathways) have been extensively investigated in the UV range, from both experimental and theoretical points of view. On the basis of the stable products observed in UV photolysis gas-phase of acetic acid, several possible dissociation processes (Fang et al 2002;Mackie & Doolan 1984;Satio et al 1990;Blake & Jackson 1969;Ausloss & Steacie 1955) were suggested:…”

“…The photodissociation of acetic acid has been studied experimentally and theoretically in the ultraviolet region (Bernstein et al 2004;Maçôas et al 2004;Fang et al 2002;Naik et al 2001;Hunnicutt et al 1989;Blake & Jackson 1969). However, despite some photoabsorption studies in the X-ray range (Robin et al 1998, and references therein) there are no studies focusing on the photodissociation pathways due to soft X-rays.…”