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Comparative Study of the Dissociative Ionization of 1,1,1 Trichloroethane Using Nanosecond and Femtosecond Laser Pulses
CSIR National Laser Centre, PO Box 395, Meiring Naude Road, Pretoria 0001, South Africa
Physics Department, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa
Chemical Resource Beneficiation, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa
* Author to whom correspondence should be addressed.
Received: 28 January 2010; in revised form: 25 February 2010 / Accepted: 26 February 2010 / Published: 17 March 2010
Abstract: Changes in the laser induced molecular dissociation of 1,1,1-trichloroethane (TCE) were studied using a range of intensities and standard laser wavelengths with nanosecond and femtosecond pulse durations. TCE contains C-H, C-C and C-Cl bonds and selective bond breakage of one or more of these bonds is of scientific interest. Using laser ionization time of flight mass spectrometry, it was found that considerable variation of fragment ion peak heights as well as changes in relative peak ratios is possible by varying the laser intensity (by attenuation), wavelength and pulse duration using standard laser sources. The nanosecond laser dissociation seems to occur via C-Cl bond breakage, with significant fragmentation and only a few large mass ion peaks observed. In contrast, femtosecond laser dissociative ionization results in many large mass ion peaks. Evidence is found for various competing dissociation and ionization pathways. Variation of the nanosecond laser intensity does not change the fragmentation pattern, while at high femtosecond intensities large changes are observed in relative ion peak sizes. The total ionization yield and fragmentation ratios are presented for a range of wavelengths and intensities, and compared to the changes observed due to a linear chirp variation.
Keywords: laser ionization; laser dissociation; coherent control; trichloroethane
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Du Plessis, A.; Strydom, C.; Botha, L. Comparative Study of the Dissociative Ionization of 1,1,1 Trichloroethane Using Nanosecond and Femtosecond Laser Pulses. Int. J. Mol. Sci. 2010, 11, 1114-1140.
Du Plessis A, Strydom C, Botha L. Comparative Study of the Dissociative Ionization of 1,1,1 Trichloroethane Using Nanosecond and Femtosecond Laser Pulses. International Journal of Molecular Sciences. 2010; 11(3):1114-1140.
Du Plessis, Anton; Strydom, Christien; Botha, Lourens. 2010. "Comparative Study of the Dissociative Ionization of 1,1,1 Trichloroethane Using Nanosecond and Femtosecond Laser Pulses." Int. J. Mol. Sci. 11, no. 3: 1114-1140.