title: Photodissociation dynamics of 2,5-dihydroxyacetophenone.
abstract: Photodissociation of 2,5-dihydroxyacetophenone (DHAP), an important matrix compound in matrix-assisted laser desorption/ionization (MALDI), was studied in a molecular beam at 193 nm using multimass ion imaging techniques. Two major dissociation channels were observed, including (1) C(6)H(3)(OH)(2)COCH(3) --> OC(6)H(3)(OH)COCH(3) + H and (2) C(6)H(3)(OH)(2)COCH(3) --> C(6)H(3)(OH)(2) + COCH(3). The minor channels include C(6)H(3)(OH)(2)COCH(3) --> C(6)H(3)(OH)(2)CO + CH(3) and/or C(6)H(3)(OH)(2)COCH(3) --> C(6)H(3)(OH)(2) + CO + CH(3). The photofragment translational energy distribution suggests that reaction 1 occurs at an excited state in which the potential along the O-H bond distance is repulsive. Comparison to the branching ratios from RRKM calculations suggests that reaction 2 does not occur at either the ground state or the triplet state or that if it does occur at one of these states it must not follow the RRKM model. A comparison to the photodissociation dynamics of acetophenone and phenol and its derivatives was made.
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica, P.O. Box 23-166, Taipei, 10617 Taiwan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Morisawa
authors.forename: Yuri A
authors.initials: YA
authors.lastname: Dyakov
authors.forename: Chien-Ming
authors.initials: CM
authors.lastname: Tseng
authors.forename: Y T
authors.initials: YT
authors.lastname: Lee
authors.forename: Chi-Kung
authors.initials: CK
authors.lastname: Ni