Time-Resolvesd Tunable Diode Laser Detection of the Products of the Infrared Multiphoton Dissociation of CF2HCl, (CF3)2CO, and CH3l3
Abstract
In the experiments described in thesis, tunable diode lasers are used to detect infrared absorption by the transient specifies produced in the infrared multiphoton dissociation (IRMPD) of CF2HCl, (CF3)2CO, and CHCL3.
The time-resolved infrared absorptions of CF2 and HOl are dected following the IRMPD of CF2HCl. Quantification of the HCl allows one to determine a CF2 infrared absorption linestrength, (9+2) x 10^-21 cm molecule^-1 for the rQ3 (9) line. From this linestrength, the CF2V1 bandstrength is found to be (3.4*0.8) x 10^-18 cm molecule^-1. The rate constant for CF2 recombination to form C2F4 is found to be (2.3+0.7) x 10^-14 cm^3 molecule^-1 s^-1.
Time-resolved detection of CF3, C2F6, and CO following the IRMPD of (CF3)2CO establishes that the dissociation mechanism involves the production of one molecule of CO and two of CF3. From this stoichiometry, the linestrength of the rH16(20)CF3 transition is found to be (1.4+0.3) x 10^-20 cm molecule^-1 and the CF3 V3 bandstrength is then calculated to be (8+2) X 10^-17 cm molecule^-1. The rate constant for CF3 recombination is measured to be (2+2+0.5) s 10^-12 cm^3 molecule^-1 s^-1 at or near the high pressure limit, while the rate constant for CF3 reacting with O2 and NO are found to be (2.1+0.5) x 10^-29 and (2.8+0.7) x 10^-29 cm^6 molecule^-2 s^-1 respectively.
The use of TDLs in determining the isotopic selectivity of the IRMPD processes is then analysed. The sensitivity of the technique is demonstrated in the detection of the DCL produced in the IRMPD of natural abundance CDCL3 in CHCl3. However, complication due to wall absorption and desorption effects necessitate monitoring the DCl and HCl on a short timescale (tens of us) to obtain meaningful quantitative information. It is shown that the CCl4 and much of the HCl produced in the photolysis of CDCL3/CHCl3 mixtures is the result of isotopically non-selective reactions involving CL atoms.