Wavelength-dependent Photodissociation Dynamics of Benzaldehyde

Abstract

The ultrafast dynamics of benzaldehyde upon 260, 271, 284, and 287 nm excitations have been studied by femtosecond pump-probe time-of-flight mass spectrometry. A bi-exponential decay component model was applied to fit the transient profiles of benzaldehyde ions and fragment ions. At the S 2 origin, the first decay of the component was attributed to the internal conversion to the high vibrational levels of S 1 state. Lifetimes of the first component decreased with increasing vibrational energy, due to the influence of high density of the vibrational levels. The second decay was assigned to the vibrational relaxation of the S 1 whose lifetime was about 600 fs. Upon 287 nm excitation, the first decay became ultrashort (∼56 fs) which was taken for the intersystem cross from S 1 to T 2 , while the second decay component was attributed to the vibrational relaxation. The pump-probe transient of fragment was also studied with the different probe intensity at 284 nm pump.

Electronic Relaxation in Benzaldehyde Evaluated via TD-DFT and Localized Diabatization: Intersystem Crossings, Conical Intersections, and Phosphorescence

“…The origin of S 1 (n−π*) is found to lie 26 919 cm –1 above the ground state with weak intensity as measured by sensitized phosphorescence excitation spectrum . Following excitation to the S 1 state, benzaldehyde undergoes a rapid ISC to the π–π* triplet state. ,− The efficiency of S 1 → T ISC is near unity in the vapor phase according to the absorption and phosphorescence excitation spectra . The two lowest triplet states, T 1 (n−π*) and T 2 (π–π*), are found lying below the S 1 state and close to each other, whereas only the n−π* triplet state has been successfully located in the gas phase. ,,,, The band origin of T 1 (n−π*) lies ∼25 180 cm –1 above the ground state from the phosphorescence excitation spectrum of isolated benzaldehyde, , which is slightly below the S 1 origin.…”

Three-Dimensional Diabatic Potential Energy Surfaces for the Photodissociation of Thiophenol

“…Due to the role as the chromophores in many biological molecules, − the photochemistry of heteroaromatic molecules such as pyrrole, imidazole, and phenol has received considerable attention in the past several decades. − The π* ← π transitions are responsible for the strong ultraviolet (UV) absorptions, which play an important role in photoprotection for humans on the earth. , Since O and S atoms have the same number of the valence electrons, the photochemistry of thiophenol and phenol is very similar in characteristics of the 1 πσ*-mediated photodissociation. There are two conical intersections (CIs) on the dissociation pathway along the S–H or O–H dissociation coordinate.…”