ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Using the laser photolysis/laser-induced fluorescence (LP/LIF) pump–probe technique, the gas phase photodissociation dynamics of room temperature DNCO were studied at photolysis wavelengths of 193 and 248 nm. D atoms produced via DNCO (X˜ 1A)+hν→D(2S)+NCO(X˜ 2Π) were detected by (2p 2P←1s 2S)-LIF using tunable narrow-band Lyman-α laser radiation (λLα(approximate)121.5 nm) generated by resonant third-order sum-difference frequency conversion of pulsed dye laser radiation. By means of a photolytic calibration method absolute cross sections for the direct photochemical D atom formation were measured to be σD(193 nm)=(5.5±0.5)×10−20 cm2 molecule−1 and σD(248 nm)=(1.2±0.2)×10−21 cm2 molecule−1. For the wavelength of 193 nm, the measurement of the optical absorption cross section σDNCO(193 nm)=(2.6±0.2)×10−19 cm2 molecule−1 allowed the direct determination of the D atom product quantum yield of φD(193 nm)=(0.21±0.03). At the wavelength of 248 nm, where the optical absorption cross section was too small to be measured with reasonable accuracy, a kinetic calibration method was used to measure product quantum yields for D atom, φD(248 nm)=(0.77±0.10), and for "spin-forbidden" ND(X 3Σ−) formation, φND(248 nm)=(0.23±0.10). From the D atom Doppler profiles, measured under collision-free conditions, the fraction of the available energy released as product translational energy was determined to be fT(D+NCO)=(0.44±0.04) for 193 nm and fT(D+NCO)=(0.64±0.17) for 248 nm photolysis wavelengths. In addition, using polarized photodissociation laser light, measurements were carried out in order to determine the anisotropy of the D atom product angular distribution. It was found that the value of the anisotropy parameter β decreases from −(0.45±0.09) for a photolysis wavelength of 193 nm to −(0.01±0.10) at 248 nm, suggesting a moderately anisotropic distribution at the shorter wavelength and an effectively isotropic one at the longer wavelength. Comparisons are made with results from recent photodissociation dynamics studies of the isotopomer HNCO. © 1997 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.473489
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