Yc. Hsu et al., 193.3 NM PHOTODISSOCIATION OF ACETYLENE - NASCENT STATE DISTRIBUTION OF CCH RADICAL STUDIED BY LASER-INDUCED FLUORESCENCE, The Journal of chemical physics, 105(20), 1996, pp. 9153-9161
The nascent rovibronic distribution of CCH radicals in the 193.3 nm ph
otolysis of acetylene has been measured by laser-induced fluorescence
in a supersonic jet. CCH fragments in the <(X)over tilde (2) Sigma(+)>
State are vibrationally hot, but rotationally cold. Predominant CCH f
ragments were observed at levels of the (X) over bar state with large
mixing of <(A)over tilde -state> character, particularly levels near t
he potential minimum of <(A)over tilde (II)-I-2>. This indicates that
a nonadiabatic transition near the exit channels plays an important ro
le in the 193.3 nm photodissociation of acetylene. Some, but not all,
of the K=1 levels have distinctively bimodal rotational distributions.
The relative vibrational energy distributions obtained from this work
were used to simulate the translational energy distribution of the hy
drogen atom by Balko, Zhang, and Lee [J. Chem. Phys. 94, 7958 (1991)]
to extract the population distribution of CCH. It is thus determined t
hat the majority of CCH radicals are formed in the ground electronic s
tate ((X) over tilde). Less than half of the CCH population was detect
ed at K=1 levels, and the rest was distributed among K=0, 2, and 3 sta
cks. The bond energy of HCC-H is estimated as 131.5+/-0.5 kcal/mol fro
m the vibronic energy of the most populated CCH fragments determined i
n this work and the translational energy of the recoiled hydrogen atom
reported previously by Balko, Zhang, and Lee and Segall, Wen, Lavi, S
inger, and Wittig [J.Phys.Chem. 95, 8078 (1991)]. (C) 1996 American In
stitute of Physics.