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Jeong BG, Choi HW, Song JK, Park SM. Branching ratio in photodissociation of 1-bromo-3-chlorobenzene cation. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2022; 271:120899. [PMID: 35104740 DOI: 10.1016/j.saa.2022.120899] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Revised: 01/06/2022] [Accepted: 01/12/2022] [Indexed: 06/14/2023]
Abstract
A new and convenient calculation method based on Rice-Ramsperger-Kassel-Marcus (RRKM) theory assuming an extremely loose transition state (LTS) has been attempted to predict the branching ratio in photodissociation. This method enables estimation of the branching ratios without detailed structural information on the transition state which is indispensable in conventional RRKM calculations. To evaluate our simple method through comparison to the experimental results, photodissociation of 1-bromo-3-chlorobenzene cation (3BCB+) was chosen as a model unimolecular reaction system which has two distinct photodissociation channels in ultraviolet region: 3BCB+ → Br-dissociated daughter ion (ClBz+) + Br and 3BCB+ → Cl-dissociated daughter ion (BrBz+) + Cl. The branching ratio was monitored with decreasing the internal energy using a linear tandem time-of-flight mass spectrometer, which clearly showed decreased branching ratios of 3BCB+ → ClBz+ + Br over 3BCB+ → BrBz+ + Cl in reasonable agreement with the calculation results employing the new method. Although there was some discrepancy in internal energy between the experimental and calculation results, the new calculation method is worth to be extended to other diverse systems considering its intuitive and simple nature.
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Affiliation(s)
- Bong Gyu Jeong
- Department of Chemistry, Kyung Hee University, Seoul 02447, Republic of Korea
| | - Hyun Wook Choi
- Department of Chemistry, Kyung Hee University, Seoul 02447, Republic of Korea
| | - Jae Kyu Song
- Department of Chemistry, Kyung Hee University, Seoul 02447, Republic of Korea.
| | - Seung Min Park
- Department of Chemistry, Kyung Hee University, Seoul 02447, Republic of Korea.
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Che DC, Kawamata H, Nakamura M, Kasai T, Lin KC. A vector correlation study using a hexapole-oriented molecular beam: photodissociation dynamics of oriented isohaloethane. Phys Chem Chem Phys 2022; 24:5914-5920. [PMID: 35195628 DOI: 10.1039/d1cp05788j] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The photodissociation dynamics of isohaloethane (1-bromo-2-chloro-1,1,2-trifluoroethane) at 234 nm was studied by a sliced imaging technique combined with an oriented molecular beam. The speed and angular distributions of the competitive products of spin-orbit selected Br and Cl atoms were determined by analysis of the obtained images. The anisotropic parameter, β, was found to be 2.0 ± 0.2 for the excited state of Br(2P1/2) (Br*) and 1.2 ± 0.3 for the ground state of Br(2P3/2) (Br). The speed distributions for both Br and Br* exhibited Gaussian-like characteristics. These results indicate that Br atoms were generated by direct formation after excitation through the nσ*(C-Br) potential energy surfaces. In contrast, the angular distributions for the Cl fragments were almost isotropic, while the speed distributions displayed Boltzmann-like characteristics. This suggests that the Cl atoms may form through long-lived parent molecules after photoexcitation. The branching ratio for Br and Cl atom formation was found to be approximately 1.2, that is, Br atom formation occurred preferentially, in contrast to the case of halothane photodissociation reported in our previous work [Che et al., J. Phys. Chem. A, 2020, 124, 5288]. A vector correlation study between the laser polarization axis and the direction of the dipole moment revealed a similar tendency for all photofragments, suggesting that the fragments were formed through a common excited state of isohaloethane. The vector correlation was also studied theoretically for comparison with the experimental results. The angle between the transition dipole moment in photodissociation and the permanent dipole moment was found to be 42 ± 15°. The obtained results indicate that this vector correlation approach combined with an oriented molecular beam is a powerful tool for determining the transition dipole moments in photodissociation.
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Affiliation(s)
- Dock-Chil Che
- Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
| | - Hiroshi Kawamata
- Center for Higher Education and Global Admissions, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Masaaki Nakamura
- Department of Chemistry, School of Science, Tokyo Institute of Technology, Meguro, Tokyo 152-8550, Japan
| | - Toshio Kasai
- Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan.,Department of Applied Physics, Osaka University, Suita, Osaka 565-0871, Japan
| | - King-Chuen Lin
- Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan.,Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
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Chang HP, Nakamura M, Kasai T, Lin KC. Photodissociation study of spatially oriented (R)-3-bromocamphor by the hexapole state selector. Mol Phys 2021. [DOI: 10.1080/00268976.2021.1985643] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- Hsiu-Pu Chang
- Department of Chemistry, National Taiwan University, Taipei, Taiwan
| | - Masaaki Nakamura
- Department of Chemistry, School of Science, Tokyo Institute of Technology, Ookayama, Meguro, Japan
| | - Toshio Kasai
- Department of Chemistry, National Taiwan University, Taipei, Taiwan
- Department of Applied Physics, Graduate School of Engineering, Osaka University, Suita, Japan
| | - King-Chuen Lin
- Department of Chemistry, National Taiwan University, Taipei, Taiwan
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
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Lin KC, Muthiah B, Chang HP, Kasai T, Chang YP. Halogen-related photodissociation in atmosphere: characterisation of atomic halogen, molecular halogen, and hydrogen halide. INT REV PHYS CHEM 2020. [DOI: 10.1080/0144235x.2020.1822590] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- King-Chuen Lin
- Department of Chemistry, National Taiwan University, Taipei, Taiwan
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
| | | | - Hsiu-Pu Chang
- Department of Chemistry, National Taiwan University, Taipei, Taiwan
| | - Toshio Kasai
- Department of Chemistry, National Taiwan University, Taipei, Taiwan
- Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan
| | - Yuan-Pin Chang
- Department of Chemistry, National Sun Yat-sen University, Kaohsiung, Taiwan
- Aerosol Science Research Center, National Sun Yat-sen University, Kaohsiung, Taiwan
- Department of Medicinal and Applied Chemistry, Kaohsiung Medical University, Kaohsiung, Taiwan
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Che DC, Nakamura M, Chang HP, Lin KC, Kasai T, Aquilanti V, Palazzetti F. UV Photodissociation of Halothane in a Focused Molecular Beam: Space-Speed Slice Imaging of Competitive Bond Breaking into Spin-Orbit-Selected Chlorine and Bromine Atoms. J Phys Chem A 2020; 124:5288-5296. [PMID: 32498517 DOI: 10.1021/acs.jpca.0c02800] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A molecular beam of halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) is focused by a hexapolar electrostatic field and photolyzed by UV laser radiation at 234 nm. Angular and speed distributions of chlorine and bromine photofragments emitted from halothane are measured for both spin-orbit states independently. Although the dissociation energy of the C-Cl bond is larger than that of C-Br, the relative yield of Cl to Br was found to be approximately 2. Measured speed and angular distributions of atomic fragments show distinct kinetic energy release and scattering characteristics: for bromine, observed fast and aligned fragments exhibit a signature of a direct mode of dissociation for the C-Br bond, via the electronically excited potential energy surface denoted nσ*(C-Br), of repulsive nature; for chlorine, a variation in the features is observed for the dissociation pathway through nσ*(C-Cl), from a modality similar to the bromine case, leading to fragments with appreciable kinetic energy release and pronounced directionality, to a modality involving slow products, nearly isotopically distributed. The origin of this behavior can be attributed to nonadiabatic interaction operating between the nσ*(C-Br) and nσ*(C-Cl) surfaces. These results are not only relevant for a detailed understanding of adiabatic versus diabatic coupling mechanisms in the manifold of excited states populated by photon absorption, but they also point out the possibility of selectively inducing specific dissociation pathways, even when involving energetically unfavorable outcomes, such as, in this case, the prevailing rupture of the stronger C-Cl bond against that of the weaker C-Br bond.
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Affiliation(s)
- Dock-Chil Che
- Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Masaaki Nakamura
- Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan
| | - Hsiu-Pu Chang
- Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan
| | - King-Chuen Lin
- Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan.,Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Toshio Kasai
- Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan.,Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
| | - Vincenzo Aquilanti
- Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, Perugia 06123, Italy.,Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, Rome 00016, Italy
| | - Federico Palazzetti
- Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, Perugia 06123, Italy
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