UC Riverside

The photodissociation dynamics of several important free radicals were studied using High-n Rydberg H-atom time-of-flight (HRTOF) technique, including the SD and CH₃S radicals which belong to the sulfur system, and C₃H₃, C₇H₇ and C₃H₅ radicals which are related to the formation of polycyclic aromatic hydrocarbons (PAHs).

The first chapter discusses the photodissociation dynamics as well as its experimental methodology. The experimental setup of the HRTOF technique is explained in detail.

The second chapter investigates the UV photodissociation dynamics of the SD radical in vibrationally ground and excited states in the photolysis wavelength region of 220 to 244 nm. The anisotropy parameter is β~ -1 while the spin-orbit branching fractions of the S(³P_J) products are essentially constant. The dissociation mechanism and the bond dissociation energy are also obtained.

The third chapter investigates the near-UV photodissociation of the thiomethoxy (CH₃S) radical at 344-362 nm. Two vibronic levels of the thiomethoxy radical dissociate to H + H₂CS, while the others in the vicinity dissociate to CH₃ + S(³P_J). H-atom angular distribution is isotropic. The dissociation mechanism is consistent with internal conversion mechanism.

The fourth chapter investigates the UV photodissociation dynamics of the propargyl (C₃H₃) radical at 230-250 nm. The photofragment yield spectra of the H + C₃H₂ product channel are in good agreement with previous UV absorption spectrum. The H + C₃H₂ product translational energy distributions are obtained as well as the dissociation mechanism. The H-atom product angular distribution is isotropic.

Chapter 5 investigates the UV photodissociation dynamics of the benzyl (C₇H₇) radical at 228-270 nm. The H-atom photofragment yield spectra are in a good agreement with the previous UV absorption spectra. The H + C₇H₆ product translational energy distributions indicate the production of fulvenallene + H. The H/D product ratios from isotope labeling studies suggest that the H/D atoms are scrambled in the photodissociation of benzyl.

Chapter 6 investigates the UV photodissociation dynamics of the allyl (C₃H₅) radical at 216-238 nm. H-atom photofragment yield spectra suggest another dissociation channel CH₃ + C₂H₂ in this region. The C₃H₄ + H product translational energy release indicate the production of allene + H or propyne + H. The product angular distribution and dissociation mechanism are also obtained.

Chapter 7 discusses the future work on several radicals: phenyl (C₆H₅) radical, 1-propenyl (CHCHCH₃) and 2-propenyl (CH₂CCH₃) radicals.