Quantum Dynamics of Photodissociation: Recent Advances and Challenges

Abstract

Recent advances in constructing accurate potential energy surfaces and nonadiabatic couplings from high-level ab initio data have revealed detailed potential landscapes in not only the ground electronic state but also excited ones. They enabled quantitatively accurate characterization of photoexcited reactive systems using quantum mechanical methods. In this Perspective, we survey the recent progress in quantum mechanical studies of adiabatic and nonadiabatic photodissociation dynamics, focusing on initial state control and product energy disposal. These new insights helped to understand quantum effects in small prototypical systems, and the results serve as benchmarks for developing more approximate theoretical methods.

Isotope Effects on State-to-State Photodissociation Dynamics of D2S in Its First Absorption Band

“…Since there exists a CI between the lowest two excited 1 A″ states at the FC region, it is necessary to carry out the quantum dynamical calculations using the quasi-diabatic representation to minimize the derivative coupling. 36,38 The quasi-diabatic Hamiltonian is given in the matrix form as (ℏ = 1),…”

“…The photodissociation of D 2 S in the first band is depicted as follows: D 2 normalS false( X̃ A 1 1 , false( v 1 , v 2 , v 3 false) , J K normala K normalc false) + h ν → D 2 normalS false( 2 A ″ 1 false) false → CI D 2 normalS false( 1 A ″ 1 false) → SD false( X̃ Π 2 , v , j false) + normalD false( S 2 false) where ( v 1 , v 2 , v 3 ) and J K a K c signify the parent ro-vibrational state of D 2 S( X̃ 1 A 1 ), with three normal mode quantum numbers denoting the symmetric stretching, bending, and antisymmetric stretching modes, respectively. Since there exists a CI between the lowest two excited 1 A ″ states at the FC region, it is necessary to carry out the quantum dynamical calculations using the quasi-diabatic representation to minimize the derivative coupling. , The quasi-diabatic Hamiltonian is given in the matrix form as (ℏ = 1), Ĥ = T̂ false( R , r , γ false) true[ .25ex2ex .25ex2ex 1 0 0 1 true] + true[ .25ex2ex .25ex2ex .25ex2ex .25ex2ex ...…”

“…The photodissociation of D 2 S in the first band is depicted as follows: where ( v 1 , v 2 , v 3 ) and J K a K c signify the parent ro-vibrational state of D 2 S­( X̃ 1 A 1 ), with three normal mode quantum numbers denoting the symmetric stretching, bending, and antisymmetric stretching modes, respectively. Since there exists a CI between the lowest two excited 1 A ″ states at the FC region, it is necessary to carry out the quantum dynamical calculations using the quasi-diabatic representation to minimize the derivative coupling. , The quasi-diabatic Hamiltonian is given in the matrix form as (ℏ = 1), in which V A , V B , and V AB are the three quasi-diabatic PESs and have been calculated in our previous work where μ R and μ r are the reduced mass for the R (D-SD) and r (SD) directions in the product Jacobi coordinates, respectively.…”

“…On the other hand, accurate potential energy surfaces (PESs) are the prerequisite of photodynamics calculations. 36 In 1993, Schinke et al 12 constructed quasi-diabatic representations for two coupled low-lying excited states of H 2 S by ab initio calculations, confirming that the dissociation proceeds via nonadiabatic transition from the initially excited bound 1 1 B 1 state to a dissociative 1 1 A 2 state. Although the ro-vibrational distributions of SD(X ̃2Π) were generally in reasonable agreement with those experimental data at 193 nm, the overall width of the broad spectral band was significantly smaller and its diffuse structures were more pronounced than those of measured ones.…”

“…The dissociation occurs promptly following a perpendicular photoexcitation, and the resulting SD fragments are formed predominantly (>99%) in their ground vibronic level. On the other hand, accurate potential energy surfaces (PESs) are the prerequisite of photodynamics calculations . In 1993, Schinke et al constructed quasi-diabatic representations for two coupled low-lying excited states of H 2 S by ab initio calculations, confirming that the dissociation proceeds via nonadiabatic transition from the initially excited bound 1 1 B 1 state to a dissociative 1 1 A 2 state.…”