The photodissociation dynamics of C[sub 2]H[sub 2] and C[sub 2]H: Detection of the C[sub 2] fragments using laser-induced fluorescence

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:7301775

Bao, Y

The UV photodissociation dynamics of acetylene has been investigated through the molecular beam and laser-induced fluorescence (LIF) techniques. In a focused ArF laser beam, the acetylene molecule dissociates via the following reactions: C[sub 2]H[sub 2] + h[nu][sub 193] nm [yields] H + C[sub 2]H; C[sub 2]H + h[nu][sub 193] nm [yields] H + C[sub 2]. Using the LIF technique, the C[sub 2] fragments have been observed in several electronic states, including the C[sub 2](A[sup 1][Pi][sub u]), C[sub 2](B[prime][sup 1][Sigma][sup +][sub g]), and C[sub 2](a[sup 3][Pi][sub u]) states. The C[sub 2](A[sup 1][Pi][sub u]) fragments are observed up to v[double prime] = 4, while the C[sub 2](B[prime][sup 1][Sigma][sup +][sub g]) up to v[double prime] = 2. The nascent rotational and vibrational distributions of these two states have been measured experimentally following the 193 nm laser photodissociation. The rotational state distributions of both states present a bimodal Boltzmann-like behavior. A combined model of the impulsive approximation and phase space theory has been developed to fit the experimental results. This model can reasonably well predict the observed rotational distributions. In addition, the rotationally-resolved LIF spectrum of the (1-0) vibrational band of the C[sup 1][Pi]-A[sup 1][Pi] transition of the isotopic [sup 12]C[sup 13]C molecule has been observed and assigned without using any [sup 13]C-enriched reagents. The C[sub 2](a[sup 3][Pi][sub u]) fragments are detected up to the v[close quotes] = 5 level. The rovibrational state distributions of this state are determined by simulating the observed LIF spectrum using a computer simulation program. Furthermore, a two-photon LIF technique has been developed for the detection of the C[sub 2](X[sup 1][Sigma][sup +][sub g]) ground state. Due to the absence of the nascent two-photon LIF signals, it may imply that this state is not one of the major fragments in the photodissociation of acetylene at 193 nm.

• Research Organization: California Univ., Davis, CA (United States)
• OSTI ID: 7301775
• Country of Publication: United States
• Language: English

Related Subjects

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