title: Fully state-resolved photodissociation of formaldehyde, H2CO --> H + HCO:K conservation and a rigorous test of statistical theories.
abstract: The photodissociation dynamics of the reaction H2CO+hnu --> H + HCO have been investigated in the range 60-400 cm(-1) above the reaction threshold. Supersonically cooled formaldehyde was excited into 15 specific J, K(a), K, rotational states i n two vibrational lev el s 2(1) 4(1) 6(1) and 2(2) 4(1) in the A(1A2) state. The laser-induced fluorescence spectra of the nascent HCO fragment provided detailed product state distributions (PSDs), resolved by N, K(a), K(c), and J. When just the overall molecular rotation N is considered the PSDs are in remarkable agreement with calculations based on phase space theory (PST). However, when the projection of N onto the molecular frame (K(a),K(c)) is included the distributions show consistent deviations from PST. In particular, there is a tendency to preserve the initial parent rotational motion about the a and b axes. The effect is that states with higher initial K(a) in H2CO produce higher final K(a) in the HCO fragment. There is also a tendency for the upper/lower members of the asymmetry doublets in H2CO to map onto the same upper/lower set of product state asymmetry doublets. Finally, there are oscillations in some of the detailed PSDs that remain unexplained.
authors.affiliation: School of Chemistry, University of Sydney, New South Wales 2006, Australia.
authors.forename: Hong-Ming
authors.initials: HM
authors.lastname: Yin
authors.forename: Klaas
authors.initials: K
authors.lastname: Nauta
authors.forename: Scott H
authors.initials: SH
authors.lastname: Kable