Multiphoton dissociation of ethyl chloride at 3. 3. mu. m: Excitation mechanism and rate equations analysis

Journal Article · Mon Dec 15 00:00:00 EST 1980 · J. Chem. Phys.; (United States)

OSTI ID:6745689

Dai, H; Kung, A H; Moore, C B

Tunable 3.3 ..mu..m laser pulses were used to excite the CH stretching modes of ethyl chloride. Energy deposition vs fluence was measured optoacoustically. For 3.3 ..mu..m excitation, absorbed energy increases almost linearly with fluence, while for 10 ..mu..m excitation there is substantial saturation. Dissociation yields were measured as a function of fluence and of wavelength by gas chromatographic determination of C/sub 2/H/sub 4/ from C/sub 2/H/sub 5/Cl+nh..nu -->..C/sub 2/H/sub 4/+HCl. Much higher yields were observed for 3.3 ..mu..m excitation than for CO/sub 2/ laser 10 ..mu..m excitation. Sharp resonances in the 3.3 ..mu..m dissociation yield spectrum match peaks in the fundamental and overtone absorption spectra. Overtone spectra show that for many rotational states the v/sub CH/=2 level (6000 cm/sup -1/) is in the quasicontinuum and that v/sub CH/=3 is always in the quasicontinuum. The resonant nature of the excitation allows the rate equations description for transitions in the quasicontinuum and continuum to be extended to the discrete levels. Absorption cross sections are estimated from ordinary IR spectra. A set of cross sections which is constant or slowly decreasing with increasing vibrational excitation gives good fits to both absorption and dissociation yield data. The much smaller dissociation yields and the saturated absorption at 10 ..mu..m reflect bottlenecking in the discrete levels. As ethyl chloride pressure is increased from 0.2 to 2 Torr the fraction dissociated decreases by nearly a factor of 2. Only about 10% further decrease occurs from 2 to 6 Torr. The rate equations model gives a similar curve when the strong collision assumption is made for vibrational relaxation and RRKM dissociation rates are used.

• Research Organization: Department of Chemistry, University of California and Materials and Molecular Research Division of the Lawrence Berkeley Laboratory, Berkeley, California 94720
• OSTI ID: 6745689
• Journal Information: J. Chem. Phys.; (United States), Vol. 73:12
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
CHLORINATED ALIPHATIC HYDROCARBONS
DISSOCIATION
ABSORPTION SPECTRA
CHEMICAL REACTION KINETICS
CHLORIDES
ETHYL RADICALS
EXCITATION
VIBRATIONAL STATES
ALKYL RADICALS
CHLORINE COMPOUNDS
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITED STATES
HALIDES
HALOGEN COMPOUNDS
HALOGENATED ALIPHATIC HYDROCARBONS
KINETICS
ORGANIC CHLORINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
RADICALS
REACTION KINETICS
SPECTRA
640302* - Atomic
Molecular & Chemical Physics- Atomic & Molecular Properties & Theory