Ultrafast dissociation dynamics of acetone: A revisit to the S1 state and 3s Rydberg state

Abstract

Because of the dispute in the literature over the dissociation rate and energy partitioning of the acetone molecule upon photoexcitation to the S 1 state (*←n) and 3s Rydberg state (3s←n), we have remeasured the lifetime of acetone ͑also d 6 -acetone͒ on the S 1 and 3s surfaces by a femtosecond time-resolved multiphoton ionization technique, coupled with a reflectron time-of-flight mass spectrometer. The measured dissociation rate of acetone on the S 1 surface is prompt, and the acetyl radical is long lived. The lifetime of acetone on the 3s surface is measured to be 3.2Ϯ0.4 ps ͑6.0Ϯ0.5 ps for d 6 -acetone͒. The dissociation rate of acetyl is approximately 1.7 ps ͑2.5 ps for d 3 -acetyl͒ from the curve fitting. This agrees well with the Rice-Ramsperger-Kassel-Marcus theory predicted lifetime of 1.0 ps ͑1.9 ps for d 3 -acetyl͒ when the internal excitation energy of the acetyl radical is treated by a statistical-adiabatic-impulsive model.

Femtochemistry of Norrish Type‐I Reactions: IV. Highly Excited Ketones—Experimental

“…Castleman and co-workers [8] studied the S 2 dynamics of acetone using pump ± probe mass spectrometry at an excitation wavelength of 390 nm (3.2 eV) and a probe wavelength of 780 nm (1.6 eV). A stepwise reaction mechanism was reported and the corresponding time constants were determined to be 3.2 (6.0) ps and 1.7 (2.5) ps from the parent and the fragment-ion signals, respectively; results for the deuterated species are shown in parentheses.…”

“…A stepwise reaction mechanism was reported and the corresponding time constants were determined to be 3.2 (6.0) ps and 1.7 (2.5) ps from the parent and the fragment-ion signals, respectively; results for the deuterated species are shown in parentheses. Using a similar pump ± probe (194 ± 388 nm or 6.4 ± 3.2 eV) combination with a one-photon excitation energy almost identical to that of Castleman and co-workers, [8] Baronavski and Owrutsky [7,9] reported the two time constants to be 4.7 (13.5) ps and 3.1 (3.0) ps from the parent and the fragment ion signals, respectively. Since the excitation in both cases are very close to the 3s 0-0 band, the available energy is not sufficient for the excited molecule to undergo either a direct surface crossing to the S 1 PES via CI1 or a prompt first a-CC bond breakage on the S 2 PES via TS1.…”

Dinámica de reacciones unimoleculares en fase gas: Desviaciones del comportamiento estadístico

“…Radical acetilo. La disociación de este radical ha sido muy estudiada, sobre todo en los últimos años [75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90] . En particular, Shibata et al 87 midieron recientemente la velocidad de disociación unimolecular en función de la energía k(E), observando que a energías cercanas al límite de disociación las constantes de velocidad eran un orden de magnitud más pequeñas que las calculadas mediante la teoría RRKM, y sugirieron que la velocidad de RVI y/o el intercambio energético vibración-rotación debía estar restringido.…”

Application of femtosecond laser mass spectrometry to the analysis of volatile organic compounds

“…The molecule can be pumped to a highly excited state, and the parent ion might dissociate to form ionic fragments. The time scale of bond cleavage is several tens of femtoseconds for molecules [28,29]. The neutral fragments cannot be ionized further because the laser pulse has ended.…”