Insights into Photodissociation Dynamics of Propionyl Chloride from ab Initio Calculations and Molecular Dynamics Simulations

Abstract

The potential energy surfaces of isomerization, dissociation, and elimination reactions for CH3CH2COCl in the S0 and S1 states have been mapped with the different ab initio calculations. Mechanistic photodissociation of CH3CH2COCl at 266 nm has been characterized through the computed potential energy surfaces, the optimized surface crossing structure, intrinsic reaction coordinate, and ab initio molecular dynamics calculations. Photoexcitation at 266 nm leads to the CH3CH2COCl molecules in the S1 state. From this state, the C-Cl bond cleavage proceeds in a time scale of picosecond in the gas phase. The barrier to the C-Cl bond cleavage on the S1 surface is significantly increased by effects of the matrix and the internal conversion to the ground state prevails in the condensed phase. The HCl eliminations as a result of internal conversion to the ground state become the dominant channel upon photodissociation of CH3CH2COCl in the argon matrix at 10 K.

Combined CASSCF and MR-CI Study on Photoinduced Dissociation and Isomerization of Acryloyl Chloride

“…18,19 In argon matrix at 10 K, the barrier to the C-Cl bond cleavage is considerably increased due to the matrix effect. 42 As a result, the internal conversion from S 1 to S 0 becomes an important process for the excited molecule to deactivate in the matrix. In addition, the S 0 and S 1 states are degenerate at large C-Cl separation.…”

“…These can be seen from the calculated rate constants in Table . The C−Cl bond cleavage was observed to be the primary dissociation channel of gaseous acryloyl chloride excited at 193 nm. , In argon matrix at 10 K, the barrier to the C−Cl bond cleavage is considerably increased due to the matrix effect . As a result, the internal conversion from S 1 to S 0 becomes an important process for the excited molecule to deactivate in the matrix.…”

Adiabatic and Nonadiabatic Bond Cleavages in Norrish Type I Reaction

“…Further evidence comes from the time-independent and -dependent quantum wavepacket simulations, which to some extent show that the nonadiabatic effect in the transition-state region is very important for correctly understanding the bond-fission mechanism of Norrish type I reaction. This nonadiabatic bond-fission picture for Norrish type I reaction is totally different from the previous one, where the bond fissions are discussed by using an adiabatic multidimensional potential energy surface. ,− , Furthermore, it is also expected that this nonadiabatic bond-fission picture is common to Norrish type I reactions of a wide variety of ketones. Finally, evaluating the branching ratio itself is outside the scope of this study and would be an interesting target for future calculations.…”

“…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.…”