Ultraviolet Photodissociation Dynamics of the Allyl Radical via the B̃(2)A1(3s), C̃(2)B2(3py), and Ẽ(2)B1(3px) Electronic Excited States.
Ultraviolet (UV) photodissociation dynamics of jet-cooled allyl radical via the B̃(2)A1(3s), C̃(2)B2(3py), and Ẽ(2)B1(3px) electronically excited states are studied at the photolysis wavelengths from 249 to 216 nm using high-n Rydberg atom time-of-flight (HRTOF) and resonance-enhanced multiphoton ionization (REMPI) techniques. The photofragment yield (PFY) spectra of the H atom products are measured using both allyl chloride and 1,5-hexadiene as precursors of the allyl radical and show a broad peak centered near 228 nm, whereas the previous UV absorption spectra of the allyl radical peak around 222 nm. This difference suggests that, in addition to the H + C3H4 product channel, another dissociation channel (likely CH3 + C2H2) becomes significant with increasing excitation energy. The product translational energy release of the H + C3H4 products is modest, with the P(ET) distributions peaking near 8.5 kcal/mol and the fraction of the average translational energy in the total excess energy, ⟨fT⟩, in the range 0.22-0.18 from 249 to 216 nm. The P(ET)'s are consistent with production of H + allene and H + propyne, as suggested by previous experimental and theoretical studies. The angular distributions of the H atom products are isotropic, with the anisotropy parameter β ≈ 0. The H atom dissociation rate constant from the pump-probe study gives a lower limit of 1 × 10(8)/s. The dissociation mechanism is consistent with unimolecular decomposition of the hot allyl radical on the ground electronic state after internal conversion of the electronically excited state.
Department of Chemistry, University of California at Riverside , Riverside, California 92521, United States.|Department of Chemistry and Biochemistry, California State University, Long Beach , Long Beach, California 90840, United States.
Yu
Y
Song
Department of Chemistry, University of California at Riverside , Riverside, California 92521, United States.|Department of Chemistry and Biochemistry, California State University, Long Beach , Long Beach, California 90840, United States.
Michael
M
Lucas
Department of Chemistry, University of California at Riverside , Riverside, California 92521, United States.|Department of Chemistry and Biochemistry, California State University, Long Beach , Long Beach, California 90840, United States.
Maria
M
Alcaraz
Department of Chemistry, University of California at Riverside , Riverside, California 92521, United States.|Department of Chemistry and Biochemistry, California State University, Long Beach , Long Beach, California 90840, United States.
Jingsong
J
Zhang
Department of Chemistry, University of California at Riverside , Riverside, California 92521, United States.|Department of Chemistry and Biochemistry, California State University, Long Beach , Long Beach, California 90840, United States.
Christopher
C
Brazier