Unraveling the Photodissociation Branching and Pathways of Methane at 118 nm by Imaging the CH₃, CH₂, and CH Fragments

Wang, Pengcheng1,2; Lin, Qiaosong1,2; Xiao, Chunlei1; Yang, Xueming1,3; Liu, Kopin1,4,5; Pan, Huilin1,3

2024-07-01

10.1021/acs.jpca.4c01914

JOURNAL OF PHYSICAL CHEMISTRY A   影响因子和分区

1089-5639

1520-5215

Under irradiation of a vacuum ultraviolet (VUV) photon, methane dissociates and yields multiple fragments. This photochemical behavior is not only of fundamental importance but also with wide-ranging implications in several branches of science. Despite that and numerous previous investigations, the product channel branching is still under debate, and the underlying dissociation mechanisms remain elusive. In this study, the photofragment imaging technique was exploited for the first time to map out the momentum and anisotropy parameter distributions of the CH3, CH2, and CH fragments at the 118 nm photolysis wavelength (10.48 eV photon energy). In conjunction with previously reported results of the H atom fragment at 121.6 nm (10.2 eV), a complete set of product channel branching in both two-body and three-body fragmentations is accurately determined. We concluded that extensive nonadiabatic transitions partake in the processes with two-body fragmentations accounting for more than 90% of overall photodissociation, for which the channel branching values for CH2 + H-2 and CH3 + H are about 0.66 and 0.25, respectively. Careful kinematic analysis enables us to untangle the intertwined triple fragmentations into the CH2(X B-3(1) and & atilde; (1)A(1)) + H + H and CH(X-2 Pi) + H + H-2 channels and to evidence their underlying sequential (or stepwise) mechanisms. With the aid of electronic correlation and prior theoretical calculations of the potential energy surfaces, the most probable or dominant dissociation pathways are elucidated. Comparisons with fragmentary reports in the literature on various photochemical aspects are also documented, and discrepancies are clarified. This comprehensive study benchmarks the VUV photochemistry of methane and advances our understanding of this important process.

SCI ; EI

英语

通讯

National Natural Science Foundation of China["22373047","22003024"] ; Guangdong Introduced Innovative RD Team Project[2019ZT08L455] ; State Key Laboratory of Molecular Reaction Dynamics grant[SKLMRD-K202408]

Chemistry ; Physics

Chemistry, Physical ; Physics, Atomic, Molecular & Chemical

WOS:001260953700001

AMER CHEMICAL SOC

20242716645074

Photodissociation ; Photolysis ; Photons ; Potential energy ; Quantum chemistry

Physical Chemistry:801.4 ; Chemical Reactions:802.2 ; Organic Compounds:804.1 ; Atomic and Molecular Physics:931.3

CHEMISTRY

Web of Science

1.Chinese Acad Sci, Dalian Inst Chem Phys, State Key Lab Mol React Dynam, Dalian 116023, Peoples R China
2.Univ Chinese Acad Sci, Beijing 100049, Peoples R China
3.Southern Univ Sci & Technol, Dept Chem, Shenzhen 518055, Peoples R China
4.Natl Sun Yat Sen Univ, Aerosol Sci Res Ctr, Kaohsiung 80424, Taiwan
5.Acad Sinica, Inst Atom & Mol Sci IAMS, Taipei 10617, Taiwan

Wang, Pengcheng,Lin, Qiaosong,Xiao, Chunlei,et al. Unraveling the Photodissociation Branching and Pathways of Methane at 118 nm by Imaging the CH₃, CH₂, and CH Fragments[J]. JOURNAL OF PHYSICAL CHEMISTRY A,2024,128:5273-5284.

Wang, Pengcheng,Lin, Qiaosong,Xiao, Chunlei,Yang, Xueming,Liu, Kopin,&Pan, Huilin.(2024).Unraveling the Photodissociation Branching and Pathways of Methane at 118 nm by Imaging the CH₃, CH₂, and CH Fragments.JOURNAL OF PHYSICAL CHEMISTRY A,128,5273-5284.

Wang, Pengcheng,et al."Unraveling the Photodissociation Branching and Pathways of Methane at 118 nm by Imaging the CH₃, CH₂, and CH Fragments".JOURNAL OF PHYSICAL CHEMISTRY A 128(2024):5273-5284.