posted on 2021-07-27, 19:08authored byVincent
J. Esposito, Tianlin Liu, Guanghan Wang, Adriana Caracciolo, Michael F. Vansco, Barbara Marchetti, Tolga N. V. Karsili, Marsha I. Lester
UV
excitation of the CH2OO Criegee intermediate across
most of the broad span of the (B 1A′)–(X 1A′) spectrum results in prompt dissociation to two
energetically accessible asymptotes: O (1D) + H2CO (X 1A1) and O (3P) + H2CO (a 3A′′). Dissociation proceeds
on multiple singlet potential energy surfaces that are coupled by
two regions of conical intersection (CoIn). Velocity map imaging (VMI)
studies reveal a bimodal total kinetic energy release (TKER) distribution
for the O (1D) + H2CO (X 1A1) products with the major and minor components accounting
for ca. 40% and ca. 20% on average of the available energy (Eavl), respectively. The unexpected low TKER
component corresponds to highly internally excited H2CO
(X 1A1) products accommodating ca. 80%
of Eavl. Full dimensional trajectory calculations
suggest that the bimodal TKER distribution of the O (1D)
+ H2CO (X 1A1) products originates
from two different dynamical pathways: a primary pathway (69%) evolving
through one CoIn region to products and a smaller component (20%)
sampling both CoIn regions enroute to products. Those that access
both CoIn regions likely give rise to the more highly internally excited
H2CO (X 1A1) products. The remaining
trajectories (11%) dissociate to O (3P) + H2CO (a 3A′′) products after traversing
through both CoIn regions. The complementary experimental and theoretical
investigation provides insight on the photodissociation of CH2OO via multiple dissociation pathways through two regions
of CoIn that control the branching and energy distributions of products.