C2H2ABSTR.INF                                     7/21/93

High-Resolution, VUV (147-201 nm) Photoabsorption Cross Sections
for C2H2 at 195 and 295 K

Peter L. Smith, Kouichi Yoshino, and W.H. Parkinson
Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA

Kenji Ito
Photon Factory, National Laboratory for High Energy Physics, Tsukuba, Japan

Glenn Stark
Physics Department, Wellesley College, MA, USA

Abstract-
   Acetylene, C2H2, plays an important role in the photochemistry of the 
atmoshperes of the giant planets, in part because of its strong absorption 
features in the 145-200 nm region where there is significant solar flux.
Accurate photoabsorption cross section data at the temperatures of 
planetary atmospheres are required for interpretation of observations and 
for reliable photochemical models.  We have measured the photoabsorption
cross sections of acetylene at 195 and 295 K in the wavelength range
147-201 nm.  (The 295 K measurements extend to 137 nm.)  The high-resolution
spectrometers employed had instrumental bandwidths smaller than those used
in previous measurements and therefore produced cross sections that are 
less influenced by instrumental effects.  Our results indicate that hot 
bands make small but significant contributions to the room temperature 
absorption spectrum of C2H2.  Photochemical models of planetary atmospheres
should employ cross sections measured at the temperatures of these 
atmospheres.

Journal of Geophysical Research, Vol. 96, No. E2, Pages 17529-17533,
     September 25, 1991