Multiple Dissociation Pathways in HNCO Decomposition Governed by Potential Energy Surface Topography

Zhiguo Zhang; Hao Wu; Zhichao Chen; Yanlin Fu; Bina Fu; Dong H Zhang; Xueming Yang; Kaijun Yuan

doi:10.1021/jacsau.3c00414

Multiple Dissociation Pathways in HNCO Decomposition Governed by Potential Energy Surface Topography

JACS Au. 2023 Sep 23;3(10):2855-2861. doi: 10.1021/jacsau.3c00414. eCollection 2023 Oct 23.

Authors

Zhiguo Zhang^{1

2}, Hao Wu^{1

3}, Zhichao Chen¹, Yanlin Fu¹, Bina Fu^{1

3

4}, Dong H Zhang^{1

3

4}, Xueming Yang^{1

3

4

5}, Kaijun Yuan^{1

3

4}

Affiliations

¹ State Key Laboratory of Molecular Reaction Dynamics and Dalian Coherent Light Source, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China.
² Key Laboratory of Functional Materials and Devices for Informatics of Anhui Educational Institutions and School of Physics and Electronic Engineering, Fuyang Normal University, Fuyang, Anhui 236041, China.
³ University of Chinese Academy of Sciences, Beijing 100049, P. R. China.
⁴ Hefei National Laboratory, Hefei 230088, China.
⁵ Department of Chemistry and Center for Advanced Light Source Research, College of Science, Southern University of Science and Technology, Shenzhen 518055, China.

Abstract

The exquisite features of molecular photochemistry are key to any complete understanding of the chemical processes governed by potential energy surfaces (PESs). It is well established that multiple dissociation pathways relate to nonadiabatic transitions between multiple coupled PESs. However, little detail is known about how the single PES determines reaction outcomes. Here we perform detailed experiments on HNCO photodissociation, acquiring the state-specific correlations of the NH (a¹Δ) and CO (X¹Σ⁺) products. The experiments reveal a trimodal CO rotational distribution. Dynamics simulations based on a full-dimensional machine-learning-based PES of HNCO unveil three dissociation pathways exclusively occurring on the S₁ excited electronic state. One pathway, following the minimum energy path (MEP) via the transition state, contributes to mild rotational excitation in CO, while the other two pathways deviating substantially from the MEP account for relatively cold and hot CO rotational state populations. These peculiar dynamics are unambiguously governed by the S₁ state PES topography, i.e., a narrow acceptance cone in the vicinity of the transition state region. The dynamical picture shown in this work will serve as a textbook example illustrating the importance of the PES topography in molecular photochemistry.