Striving To Understand the Photophysics and Photochemistry of Thiophosgene: A Combined CASSCF and MR−CI Study

Ultraviolet photodissociation (UVPD) experiments of protonated tryptamine ([Tryp+H]+) have been implemented by a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer combined with a wavelength-tunable optical parametric oscillator (OPO) laser. UVPD mass spectra under different laser wavelengths have been obtained, in which the dependence of the yield of fragment ions on the laser wavelength was observed. The UVPD spectrum of [Tryp+H]+ has been obtained in the range of 210–310 nm. Besides the previously reported two competitive channels of H loss and NH3 loss, two important channels of losing CH2NH and CH2NH2 units were observed and further studied by UV–UV tandem mass spectrometry and theoretical calculations. Interestingly, results show that the pair of competitive channels of CH2NH loss and CH2NH2 loss are both from the McLafferty-type rearrangement caused by ππ* electronic excited states. After the excitation, the two different dissociation pathways produce two different ion–neutral complexes, respectively. The wavelength-dependent dissociation and the existing competitive channels shown in this study reflect the diversity of UVPD processes of such organic molecules.

Section: Introductionmentioning

confidence: 99%

Wavelength-Dependent Ultraviolet Photodissociation of Protonated Tryptamine

Zhang

Zhou

et al. 2020

“…Compared with aliphatic and aromatic carbonyl compounds, cyclic carbonyl compounds gain few studies in photodissociation dynamics. [9][10][11][12][13][14] Cyclopropanone, the simplest cyclic carbonyl compound, has a unique characteristic, strong ring-tension, and thus the ringopening reaction can easily occur not only on the ground state but also on the excited states. This characteristic increases the difficulty of understanding its photodissociation dynamics because this strong ring tension might significantly change the photodissociation mechanism, making it different from those of aliphatic and aromatic carbonyl compounds.…”

Section: Introductionmentioning

confidence: 99%

Conical Intersection Is Responsible for the Fluorescence Disappearance below 365 nm in Cyclopropanone

Cui

Fang

2009

The photodissociation dynamics of cyclopropanone was explored with the complete active space self-consistent field (CASSCF) calculations and ab initio nonadiabatic molecular dynamics simulations. The related minima, transition state (TS) and minimum-energy conical intersections (MECIs) were obtained as well as energetics. In the static CASSCF calculations, one MECI was found to be responsible for the fluorescence disappearance below 365 nm because the ultrafast internal conversion (IC) via this MECI deprived the opportunity of the fluorescence emission. Further evidence of this ultrafast IC event came from the subsequent ab initio nonadiabatic molecular dynamics simulations.

“…Thus, the multireference configuration interaction with single- and double-excitations (MRCI-SD) method is used to refine the energetics of the CASSCF(10,8)/cc-pVDZ optimized structures with zero point energy (ZPE) correction at the CASSCF(10,8)/cc-pVDZ level. This MRCI-SD//CASSCF scheme can perform well for the photodissociation dynamics of carbonyl compounds. − ,− ,− In addition, the vertical excitation energy is calculated using the linear-response time-dependent density functional theory (TDDFT) method, the equation of motion coupled-cluster (EOM-CCSD) method, and the MRCI-SD method. All of the TDDFT and CASSCF calculations are carried out by using GAUSSIAN03, while the EOM-CCSD calculations make use of GAUSSIAN09.…”

Section: Methodsmentioning

confidence: 99%

Adiabatic and Nonadiabatic Bond Cleavages in Norrish Type I Reaction

Cui

Fang

2011

One of the fundamental photoreactions for ketones is Norrish type I reaction, which has been extensively studied both experimentally and theoretically. Its α bond-cleavage mechanisms are usually explained in an adiabatic picture based on the involved excited-state potential energy surfaces, but scarcely investigated in terms of a nonadiabatic picture. In this work, the S(1) α bond-cleavage reactions of CH(3)OC(O)Cl have been investigated by using the CASSCF and MRCI-SD calculations, and the ab initio based time-dependent quantum wavepacket simulation. The numerical results indicate that the photoinduced dissociation dynamics of CH(3)OC(O)Cl could exhibit strong nonadiabatic bond-fission characteristics for the S(1) α C-Cl bond cleavage, while the dynamics of the S(1) α C-O bond cleavage is mainly of adiabatic characteristics. This nonadiabatic mechanism for Norrish type I reaction of CH(3)OC(O)Cl is uncovered for the first time. The quantum wavepacket dynamics, based on the reduced-dimensional coupled potential energy surfaces, to some extent illustrates the significance of the nonadiabatic effect in the transition-state region on the dynamics of Norrish type I reaction.