Photodissociation dynamics of the C[sub 2]H radical at 193. 3 and 212. 8 nm

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1993

OSTI ID:7267180

Urdahl, R S

A series of photolysis experiments are described which focus on identifying and characterizing the processes that regulate the dynamics of ethynyl dissociation at 193.3 and 212.8 nm. The C[sub 2]H radicals are produced via the photodissociation of acetylene, which is cooled by supersonic expansion or maintained at 300 K in a low pressure static gas cell. The decomposition of C[sub 2]H is probed under collision-free conditions by measuring the rotational quantum state distributions, within selected vibronic levels, of the resulting C[sub 2] fragments using laser-induced fluorescence (LIF). The first observation of C[sub 2]B[prime][sup 1][Sigma][sub g] [sup +], [nu] = 0,1,2) radicals in the 193.3 nm multiphoton dissociation of jet-cooled acetylene is reported. This experiment forms the basis for a novel spectroscopic approach to measuring [Delta]H[sub f,0](C[sub 2]) and D[sub 0](CC-H0). The values of these important thermodynamic quantities have been improved, and are determined here to lower levels of uncertainty than those obtained previously using other methods. Relative (C[sub 2](B[prime][sup 1][Sigma][sub g][sup +]) rotational populations are derived from the experimental LIF spectra and compared to populations calculated for this fragment based on the impulsive approximation and phase space theory. Reasonable agreement between experiment and theory is obtained when the models are combined. A set of three previously undetected spectral bands, observed for the first time while recording the saturated LIF spectrum of the C[sub 2](B[prime][sup 1][Sigma][sub g][sup +]) radical, are presented. The production of highly vibrationally excited C[sub 2](a[sup 3][Pi][sub u]) fragments during the photodissociation of C[sub 2]H at 193.3 has been verified. Results from photolysis experiments performed at 212.8 nm are used to predict the symmetry of the C[sub 2]H electronic states involved in the secondary dissociated process.

• Research Organization: California Univ., Davis, CA (United States)
• OSTI ID: 7267180
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
ACETYLENE
ALKYNES
CHEMICAL REACTIONS
DECOMPOSITION
EMISSION SPECTROSCOPY
ENERGY LEVELS
EXCITED STATES
FLUORESCENCE SPECTROSCOPY
HYDROCARBONS
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
RADICALS
ROTATIONAL STATES
SPECTROSCOPY
VIBRATIONAL STATES