1 research outputs found
Photoproduct Channels from BrCD<sub>2</sub>CD<sub>2</sub>OH at 193 nm and the HDO + Vinyl Products from the CD<sub>2</sub>CD<sub>2</sub>OH Radical Intermediate
We present the results of our product branching studies
of the
OH + C<sub>2</sub>D<sub>4</sub> reaction, beginning at the CD<sub>2</sub>CD<sub>2</sub>OH radical intermediate of the reaction, which
is generated by the photodissociation of the precursor molecule BrCD<sub>2</sub>CD<sub>2</sub>OH at 193 nm. Using a crossed laser-molecular
beam scattering apparatus with tunable photoionization detection,
and a velocity map imaging apparatus with VUV photoionization, we
detect the products of the major primary photodissociation channel
(Br and CD<sub>2</sub>CD<sub>2</sub>OH), and of the secondary dissociation
of vibrationally excited CD<sub>2</sub>CD<sub>2</sub>OH radicals (OH,
C<sub>2</sub>D<sub>4</sub>/CD<sub>2</sub>O, C<sub>2</sub>D<sub>3</sub>, CD<sub>2</sub>H, and CD<sub>2</sub>CDOH). We also characterize
two additional photodissociation channels, which generate HBr + CD<sub>2</sub>CD<sub>2</sub>O and DBr + CD<sub>2</sub>CDOH, and measure
the branching ratio between the C–Br bond fission, HBr elimination,
and DBr elimination primary photodissociation channels as 0.99:0.0064:0.0046.
The velocity distribution of the signal at <i>m</i>/<i>e</i> = 30 upon 10.5 eV photoionization allows us to identify
the signal from the vinyl (C<sub>2</sub>D<sub>3</sub>) product, assigned
to a frustrated dissociation toward OH + ethene followed by D-atom
abstraction. The relative amount of vinyl and Br atom signal shows
the quantum yield of this HDO + C<sub>2</sub>D<sub>3</sub> product
channel is reduced by a factor of 0.77 ± 0.33 from that measured
for the undeuterated system. However, because the vibrational energy
distribution of the deuterated radicals is lower than that of the
undeuterated radicals, the observed reduction in the water + vinyl
product quantum yield likely reflects the smaller fraction of radicals
that dissociate in the deuterated system, not the effect of quantum
tunneling. We compare these results to predictions from statistical
transition state theory and prior classical trajectory calculations
on the OH + ethene potential energy surface that evidenced a roaming
channel to produce water + vinyl products and consider how the branching
to the water + vinyl channel might be sensitive to the angular momentum
of the β-hydroxyethyl radicals