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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 2, Number 2
BKCSDE 2(2)
February 20, 1981 

 
Title
Vacuum Ultraviolet Photolysis of Ethyl Bromide at 104.8 - 106.7 nm
Author
Hong Lae Kim, Hee Soo Yoo, Kyung-Hoon Jung
Keywords
Abstract
Vacuum ultraviolet photolysis of ethyl bromide was studied at 104.8-106.7 nm (11.4-11.6 eV) in the pressure range of 0.2-18.6 torr at 25℃ using an argon resonance lamp with and without additives, i.e., NO and He. Since the ionization potential of CH3CH2Br is lower than the photon energy, the competitive processes between the photoionization and the photodecomposition were also investigated. The observations indicated that 50% of absorbed light leads to the former process and the rest to the latter one. In the absence of NO the principal reaction products for the latter process were found to be CH4, C2H2, C2H4, C2H6, and C3H8. The product quantum yields of these reaction products showed two strikingly different phenomena with an increase in reactant pressure. The major products, C2H4 and C2H6, showed positive effects with pressure whereas the effects on minor products were negative in both cases, i.e., He and reactant pressures. Addition of NO completely suppresses the formation of all products except C2H4 and reduces the C2H4 quantum yield. These observations are interpreted in view of existence of two different electronically excited states. The initial formation of short-lived Rydberg transition state undergoes HBr molecular elimination and this state can across over by collisional induction to a second excited state which decomposes exclusively by carbon-bromine bond fission. The estimated lifetime of the initial excited state was ∼4×10-10 sec. The extinction coefficient for CH3CH2Br at 104.8-106.7 nm and 25℃ was determined to be ε = (1/PL)ln(I0/It) = 2061±160 atm-1cm-1 with 95% confidence level.
Page
71 - 75
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