The UV-photodissociation of jet-cooled nitrosobenzene studied by fluorescence excitation spectroscopy of the NO fragment†
Abstract
Monomeric nitrosobenzene was cooled in a supersonic jet and
photolyzed with a tunable laser by excitation into the first and second UV
absorption bands corresponding to the second and higher excited singlet states
(Sn, n2). The populations of the rotational
and vibrational states of the NO fragment were probed by fluorescence excitation
spectroscopy with a second laser. No alignment of the photofragment could
be observed, and the Doppler profiles indicate an isotropic velocity distribution.
It is concluded that the dissociation occurs after fast internal conversion
to the potential energy surfaces of the electronic states S0 or
S1 which correlate both with the electronic ground states of the
products. A strong preference for the A″ component of the Λ-doublets
is observed. If orbital symmetry is conserved, the plane of rotation of the
NO fragment is perpendicular to the plane of the phenyl radical, i.e.
dissociation occurs from a highly excited torsional state in a propeller-like
motion.