The dynamics of the photolysis reaction, CFBr+h
ν→CF+Br, have been investigated for photolysis energies in the range, = 23 500–26 000 cm−1
(λ=385–435 nm). These energies correspond to excitation into the (1A″)
state of CFBr with 2500–5000 cm−1
of excess vibrational energy. Following dissociation of jet-cooled CFBr, the internal energy (Ω, Λ, J
) of the nascent CF fragments (X 2Π, υ = 0)
was probed by laser induced fluorescence spectroscopy. Two distinct types of product state distributions were observed. At energies above T00+3360 cm−1
the populations of the 2Π1/2
spin–orbit states of CF were equal, while A″
lambda doublet states were preferred over A′.
These populations are consistent with a direct dissociation mechanism on the
state, over a barrier with a height of 3360 cm−1.
The strong state mixing in the vicinity of the barrier ensures a statistical mixture of final spin–orbit states. The preference for the A″
lambda doublet states is consistent with the two lone electrons in in-plane orbitals pairing up in the final CF product, leaving one unpaired electron in an out-of-plane orbital, lying parallel to the J
vector of the recoiling fragment. For excitation at energies below T00+3360 cm−1
the ground spin–orbit state of CF (2Π1/2)
is preferred, while the lambda doublet populations are equal. The interpretation of these populations is that at these energies
state CFBr is stable with respect to dissociation over the barrier. The molecule crosses to either the
state where it encounters a deep attractive potential well. The subsequent slower dissociation rate allows the molecule to follow a more adiabatic pathway producing the lowest spin–orbit state of CF, and for any preference for lambda doublet states to be lost. © 1999 American Institute of Physics.