Ion cyclotron resonance studies of vibrationally excited ions. I. Low intensity multiphoton dissociation of gas phase ions using CW CO_2 laser radiation. II. Infrared radiative stabilization of energized species in the gas phase.

Citation

Woodin, Richard Lawrence (1979) Ion cyclotron resonance studies of vibrationally excited ions. I. Low intensity multiphoton dissociation of gas phase ions using CW CO_2 laser radiation. II. Infrared radiative stabilization of energized species in the gas phase. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/cggh-sb21. https://resolver.caltech.edu/CaltechTHESIS:11052009-133235754

Abstract

This thesis is divided into two general topics; vibrational excitation of gas phase molecules using cw CO_2 laser radiation (Chapters II and III) and stabilization of chemically activated species by infrared radiative emission (Chapters IV-VI). Chapter I is a brief introduction to the topics discussed in Chapters II- VI. Multiphoton dissociation of molecules is observed using low intensity (1-100 W cm^(-2)) cw CO_2 laser radiation. Ion cyclotron resonance techniques allow gas phase ions to be stored and irradiated for times approaching several seconds prior to mass analysis. Chapter II describes multiphoton dissociation of ions derived from diethyl ether [(C_2H_5)_2O] while Chapter III describes multiphoton dissociation of C_3F_6^+ from perfluoropropylene (C_3F_6). Energy fluence thresholds and cross-sections for multiphoton dissociation measured using low intensity radiation qualitatively agree with similar measurements using megawatt pulsed infrared lasers. For all ions which photodissociate only the lowest activation energy process is observed. Effects of bimolecular interactions, varying laser intensity, and laser wavelength on photodissociation probabilities are explored. At high pressures collisions are observed to deactivate vibrationally excited ions. At low pressures, however, C_3F_6^+ photodissociation is enhanced by collisions. The consequences of collisional enhancement of multiphoton absorption are discussed. ICR techniques are uniquely suited for studying ion-molecule reactions under nearly collisionless conditions. Chapters IV and V discuss direct association reactions of Li^+ with (C_2H_5)_2CO, CH_3COC_2H_5, (CH_3)_2CO, (CD_3)_2CO, CH_3CHO, and H_2CO at pressures low enough (< 10^(-6) Torr) to preclude collisional stabilization of the chemically activated adduct. The stabilization mechanism is assumed to be via infrared emission, and calculated attachment rates are in good agreement with experiment. In experiments similar to those described above, rates of direct electron attachment to C_6F_6 (perfluorobenzene), C_7F_8 (perfluorotoluene), c-C_4F_8 (perfluorocyclobutane), and C_7F_(14) (perfluoromethylcyclohexane) are measured at low pressure by ICR techniques. Rate constants measured by ICR are found to be one to two orders of magnitudes smaller than high pressure swarm measurements. The results are discussed in terms of radiative stabilization at low pressure versus collisional stabilization at high pressure. Combination of data from time-of-flight, electron beam-swarm, and ICR experiments allows estimates of infrared radiative lifetimes to be made. These fall in the range 0. 4-3. 0 msec, which are typical of infrared radiative processes. Data are also presented for dissociative electron attachment of CCl_4.

Thesis Files