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Zhang YR, Yuan DF, Wang LS. Probing Dipole-Bound States Using Photodetachment Spectroscopy and Resonant Photoelectron Imaging of Cryogenically Cooled Anions. J Phys Chem Lett 2023; 14:7368-7381. [PMID: 37565830 DOI: 10.1021/acs.jpclett.3c01994] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/12/2023]
Abstract
Molecular anions with polar neutral cores can support highly diffuse dipole-bound states below their detachment thresholds due to the long-range charge-dipole interaction. Such nonvalence states constitute a special class of excited electronic states for anions and were observed in early photodetachment experiments to measure the electron affinities of organic radicals. Recent experimental advances, in particular, the ability to create cold anions using a cryogenically cooled Paul trap, have allowed the investigation of dipole-bound excited states at a new level. For the first time, the zero-point level of dipole-bound excited states can be observed via resonant two-photon detachment, and resonant photoelectron spectroscopy can be performed via the above-threshold vibrational levels (Feshbach resonances) of the dipole-bound states. This Perspective describes recent progress in the investigation of dipole-bound states in the authors' lab using an electrospray photoelectron spectroscopy apparatus equipped with a cryogenically cooled Paul trap and high-resolution photoelectron imaging.
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Affiliation(s)
- Yue-Rou Zhang
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Dao-Fu Yuan
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
- Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, China
| | - Lai-Sheng Wang
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
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Abstract
Polar molecules can bind an electron in a diffuse orbital due to the charge-dipole interaction. Electronic excited states of polar molecules can also bind an electron to form core-excited dipole-bound states (DBSs), analogous to core-excited Rydberg states. However, core-excited DBSs have not been observed because of the complicated electronic structure of molecular systems. Here, we report the observation of a core-excited DBS in the pyrazolide anion as a result of the favorable electronic structure of the neutral pyrazolyl core, which has a low-lying excited state (Ã2B1) only 266 cm-1 above its ground state (X̃2A2). The binding energy of the DBS associated with the ground state is measured to be 221 cm-1, while that of the core-excited DBS is 276 cm-1, which is still a bound state relative to the detachment threshold. Vibrational Feshbach resonances are observed for both DBSs, and their autodetachment behaviors are studied by resonant photoelectron imaging.
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Affiliation(s)
- Yue-Rou Zhang
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Dao-Fu Yuan
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Lai-Sheng Wang
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
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Cao W, Zhang H, Yuan Q, Zhou X, Kass SR, Wang XB. Observation and Exploitation of Spin-Orbit Excited Dipole-Bound States in Ion-Molecule Clusters. J Phys Chem Lett 2021; 12:11022-11028. [PMID: 34739238 DOI: 10.1021/acs.jpclett.1c03309] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
We report an observation of spin-orbit excited dipole-bound states (DBSs) in arginine-iodide complexes (Arg·I-) by using temperature-dependent, wavelength-resolved "iodide-tagging" negative ion photoelectron spectroscopy. The observed DBSs are bound to the spin-orbit excited I(2P1/2) level of the neutral Arg·I complex in zwitterionic conformations and identified based on the resonant enhancement due to spin-orbit electronic autodetachment from the I(2P1/2) DBS to the I(2P3/2) neutral ground state. The observed DBS binding energies are correlated to the dipole moments of neutral Arg·I isomers and tautomers. This work thus demonstrates a new and generic spectroscopic approach to identify ion-molecule cluster conformations based on their distinguishable dipole moments.
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Affiliation(s)
- Wenjin Cao
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Hanhui Zhang
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
- Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, P.R. China
| | - Qinqin Yuan
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Xiaoguo Zhou
- Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, P.R. China
| | - Steven R Kass
- Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Xue-Bin Wang
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
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Zhang YR, Yuan DF, Qian CH, Wang LS. Observation of a dipole-bound excited state in 4-ethynylphenoxide and comparison with the quadrupole-bound excited state in the isoelectronic 4-cyanophenoxide. J Chem Phys 2021; 155:124305. [PMID: 34598564 DOI: 10.1063/5.0065510] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Negative ions do not possess Rydberg states but can have Rydberg-like nonvalence excited states near the electron detachment threshold, including dipole-bound states (DBSs) and quadrupole-bound states (QBSs). While DBSs have been studied extensively, quadrupole-bound excited states have been more rarely observed. 4-cyanophenoxide (4CP-) was the first anion observed to possess a quadrupole-bound exited state 20 cm-1 below its detachment threshold. Here, we report the observation of a DBS in the isoelectronic 4-ethynylphenoxide anion (4EP-), providing a rare opportunity to compare the behaviors of a dipole-bound and a quadrupole-bound excited state in a pair of very similar anions. Photodetachment spectroscopy (PDS) of cryogenically cooled 4EP- reveals a DBS 76 cm-1 below its detachment threshold. Photoelectron spectroscopy (PES) at 266 nm shows that the electronic structure of 4EP- and 4CP- is nearly identical. The observed vibrational features in both the PDS and PES, as well as autodetachment from the nonvalence excited states, are also found to be similar for both anions. However, resonant two-photon detachment (R2PD) from the bound vibrational ground state is observed to be very different for the DBS in 4EP- and the QBS in 4CP-. The R2PD spectra reveal that decays take place from both the DBS and QBS to the respective anion ground electronic states within the 5 ns detachment laser pulse due to internal conversion followed by intramolecular vibrational redistribution and relaxation, but the decay mechanisms appear to be very different. In the R2PD spectrum of 4EP-, we observe strong threshold electron signals, which are due to detachment, by the second photon, of highly rotationally excited anions resulted from the decay of the DBS. On the other hand, in the R2PD spectrum of 4CP-, we observe well-resolved vibrational peaks due to the three lowest-frequency vibrational modes of 4CP-, which are populated from the decay of the QBS. The different behaviors of the R2PD spectra suggest unexpected differences between the relaxation mechanisms of the dipole-bound and quadrupole-bound excited states.
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Affiliation(s)
- Yue-Rou Zhang
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA
| | - Dao-Fu Yuan
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA
| | - Chen-Hui Qian
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA
| | - Lai-Sheng Wang
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA
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Kang DH, Kim J, Cheng M, Kim SK. Mode-Specific Autodetachment Dynamics of an Excited Non-valence Quadrupole-Bound State. J Phys Chem Lett 2021; 12:1947-1954. [PMID: 33591762 DOI: 10.1021/acs.jpclett.1c00169] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The autodetachment dynamics of vibrational Feshbach resonances of the quadrupole-bound state (QBS) for the first time has been investigated in real time for the first excited state of the 4-cyanophenoxide (4-CP) anion. Individual vibrational resonances of the cryogenically cooled 4-CP QBS have been unambiguously identified, and their autodetachment rates state-specifically measured using the picosecond time-resolved pump-probe technique employing the photoelectron velocity-map imaging method. The autodetachment lifetime (τ) is found to be strongly dependent on mode, giving τ values of ∼56, ∼27, and ≤2.8 ps for the 12'1 (Evib = 406 cm-1), 12'2 (Evib = 806 cm-1), and 21'1 (Evib = 220 cm-1) modes, respectively. The striking mode-specific behavior of the QBS lifetime has been invoked by the physical model in which the loosely bound electron falls off by the dynamic wobbling of the three-dimensional quadrupole moment ellipsoid associated with the corresponding vibrational motion in the autodetachment process.
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Affiliation(s)
- Do Hyung Kang
- Department of Chemistry, KAIST, Daejeon 34141, Republic of Korea
| | - Jinwoo Kim
- Department of Chemistry, KAIST, Daejeon 34141, Republic of Korea
| | - Min Cheng
- Department of Chemistry, KAIST, Daejeon 34141, Republic of Korea
- Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Sang Kyu Kim
- Department of Chemistry, KAIST, Daejeon 34141, Republic of Korea
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Yuan DF, Liu Y, Qian CH, Kocheril GS, Zhang YR, Rubenstein BM, Wang LS. Polarization of Valence Orbitals by the Intramolecular Electric Field from a Diffuse Dipole-Bound Electron. J Phys Chem Lett 2020; 11:7914-7919. [PMID: 32898418 DOI: 10.1021/acs.jpclett.0c02514] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The diffuse electron in a dipole-bound state is spatially well separated from the valence electrons and is known to have negligible effects on the dipole-bound state's molecular structure. Here, we show that a dipole-bound state is observed in deprotonated 4-(2-phenylethynyl)-phenoxide anions, 348 cm-1 below the anion's detachment threshold. The photodetachment of the dipole-bound electron is observed to accompany a simultaneous shakeup process in valence orbitals in this aromatic molecular anion. This shakeup process is due to configuration mixing as a result of valence orbital polarization by the intramolecular electric field of the dipole-bound electron. This observation suggests that dipole-bound anions can serve as a new platform to probe how oriented electric fields influence the valence electronic structure of polyatomic molecules.
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Affiliation(s)
- Dao-Fu Yuan
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Yuan Liu
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Chen-Hui Qian
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - G Stephen Kocheril
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Yue-Rou Zhang
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Brenda M Rubenstein
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Lai-Sheng Wang
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
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Wang YT, Ning CG, Liu HT, Wang LS. High-Resolution Photoelectron Imaging and Photodetachment Spectroscopy of Cryogenically Cooled IO –. J Phys Chem A 2020; 124:5720-5726. [DOI: 10.1021/acs.jpca.0c04080] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Yong-Tian Wang
- Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Chuan-Gang Ning
- Department of Physics, State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084, P. R. China
| | - Hong-Tao Liu
- Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, P. R. China
| | - Lai-Sheng Wang
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
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Qian CH, Zhu GZ, Zhang YR, Wang LS. Photodetachment spectroscopy and resonant photoelectron imaging of the 2-naphthoxide anion via dipole-bound excited states. J Chem Phys 2020; 152:214307. [DOI: 10.1063/5.0011234] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Affiliation(s)
- Chen-Hui Qian
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA
| | - Guo-Zhu Zhu
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA
| | - Yue-Rou Zhang
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA
| | - Lai-Sheng Wang
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA
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Dobulis MA, Thompson MC, Patros KM, Sommerfeld T, Jarrold CC. Emerging Nonvalence Anion States of [Isoprene-H·]·H 2O Accessed via Detachment of OH -·Isoprene. J Phys Chem A 2020; 124:2279-2287. [PMID: 32091900 DOI: 10.1021/acs.jpca.0c01250] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The anion photoelectron imaging spectra of an ion with m/z 85, generated under ion source conditions that optimize •OH production in a coexpansion with isoprene, are presented and analyzed with supporting calculations. A spectroscopic feature observed at a vertical electron detachment energy of 2.45 eV, which dominates the photoelectron spectrum measured at 3.495 eV photon energy, is consistent with the OH-·isoprene ion-molecule complex, while additional signal observed at lower electron binding energy can be attributed to other constitutional isomers. However, spectra measured over a 2.2-2.6 eV photon energy range, i.e., from near threshold of the predominant OH-·isoprene detachment feature through the vertical detachment energy, exhibit sharp features with common electron kinetic energies, suggesting autodetachment from a temporary anion prepared by photoexcitation. The photon energy independence of the electron kinetic energy of these features along with the low dipole moment predicted for the neutral •OH·isoprene van der Waals complex, suggest a complex photon-driven process. We present calculations supporting a hypothesis that near-threshold production of the •OH···isoprene reactive complex results in hydrogen abstraction of the isoprene molecule. The newly formed activated complex anion supports a dipole bound state that temporarily traps the near zero-kinetic energy electron and then autodetaches, encoding the low-frequency modes of the dehydrogenated neutral isoprene radical in the electron kinetic energies.
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Affiliation(s)
- Marissa A Dobulis
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States
| | - Michael C Thompson
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States
| | - Kellyn M Patros
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States
| | - Thomas Sommerfeld
- Department of Chemistry and Physics, Southeast Louisiana University, SLU 10878, Hammond, Louisiana 70402, United States
| | - Caroline Chick Jarrold
- Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405, United States
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Qian CH, Zhu GZ, Wang LS. Probing the Critical Dipole Moment To Support Excited Dipole-Bound States in Valence-Bound Anions. J Phys Chem Lett 2019; 10:6472-6477. [PMID: 31589447 DOI: 10.1021/acs.jpclett.9b02679] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We report photodetachment spectroscopy and high-resolution photoelectron imaging of para-halogen substituted phenoxide anions, p-XC6H4O- (X = F, Cl, Br, I). The dipole moments of the p-XC6H4O neutral radicals increase from 2.56 to 3.19 D for X = F to I, providing a series of similar molecules to allow the examination of charge-dipole interactions by minimizing molecule-dependent effects. Excited DBSs ([XC6H4O]*-) are observed for the four anions with binding energies of 8, 11, 24, and 53 cm-1, respectively, for X = F to I, below their respective detachment thresholds. The binding energies exhibit a linear correlation with the dipole moments of the neutral radicals, extrapolating to a critical dipole moment of 2.5 D for zero binding energy. Because of the small binding energy of the excited DBS of [FC6H4O]*-, rotational autodetachment is observed to compete with vibrational autodetachment in the resonant photoelectron spectra, resulting in electrons with near zero kinetic energies.
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Affiliation(s)
- Chen-Hui Qian
- Department of Chemistry , Brown University , Providence , Rhode Island 02912 , United States
| | - Guo-Zhu Zhu
- Department of Chemistry , Brown University , Providence , Rhode Island 02912 , United States
| | - Lai-Sheng Wang
- Department of Chemistry , Brown University , Providence , Rhode Island 02912 , United States
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Zhu GZ, Wang LS. High-resolution photoelectron imaging and resonant photoelectron spectroscopy via noncovalently bound excited states of cryogenically cooled anions. Chem Sci 2019; 10:9409-9423. [PMID: 32055317 PMCID: PMC6984392 DOI: 10.1039/c9sc03861b] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2019] [Accepted: 09/16/2019] [Indexed: 01/12/2023] Open
Abstract
Valence-bound anions with polar neutral cores (μ > ∼2.5 D) can support dipole-bound excited states below the detachment threshold. These dipole-bound states (DBSs) are highly diffuse and the weakly bound electron in the DBS can be readily autodetached via vibronic coupling. Excited DBSs can be observed in photodetachment spectroscopy using a tunable laser. Tuning the detachment laser to above-threshold vibrational resonances yields vibrationally enhanced resonant photoelectron spectra, which are highly non-Franck-Condon with much richer vibrational information. This perspective describes recent advances in the studies of excited DBSs of cryogenically cooled anions using high-resolution photoelectron imaging (PEI) and resonant photoelectron spectroscopy (rPES). The basic features of dipole-bound excited states and highly non-Franck-Condon resonant photoelectron spectra will be discussed. The power of rPES to yield rich vibrational information beyond conventional PES will be highlighted, especially for low-frequency and Franck-Condon-inactive vibrational modes, which are otherwise not accessible from non-resonant conventional PES. Mode-selectivity and intra-molecular rescattering have been observed during the vibrationally induced autodetachment. Conformer-specific rPES is possible due to the different dipole-bound excited states of molecular conformers with polar neutral cores. For molecules with μ ≪ 2.5 D or without dipole moments, but large quadrupole moments, excited quadrupole-bound states can exist, which can also be used to conduct rPES.
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Affiliation(s)
- Guo-Zhu Zhu
- Department of Chemistry , Brown University , Providence , RI 02912 , USA .
| | - Lai-Sheng Wang
- Department of Chemistry , Brown University , Providence , RI 02912 , USA .
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Castellani ME, Anstöter CS, Verlet JRR. On the stability of a dipole-bound state in the presence of a molecule. Phys Chem Chem Phys 2019; 21:24286-24290. [PMID: 31663558 DOI: 10.1039/c9cp04942h] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Dipole-bound states (DBSs) are diffuse non-valence molecular orbitals of anions where the electron is bound by the permanent dipole moment of the neutral core. Here, an experimental study of the stability of such orbitals under the influence of a perturbing molecular alkyl chain is presented. Photodetachment action and photoelectron imaging spectroscopy of five para-substituted phenolate anions with progressively longer alkyl chains show that the DBS survives in all cases, suggesting that the perturbation of the orbital is not critical to the existence of the DBS.
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Zhu GZ, Cheung LF, Liu Y, Qian CH, Wang LS. Resonant Two-Photon Photoelectron Imaging and Intersystem Crossing from Excited Dipole-Bound States of Cold Anions. J Phys Chem Lett 2019; 10:4339-4344. [PMID: 31314535 DOI: 10.1021/acs.jpclett.9b01743] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We report the observation of a dipole-bound state (DBS) 659 cm-1 below the electron detachment threshold of cryogenically cooled deprotonated 4,4'-biphenol anion (bPh-) and 19 of its lowest vibrational levels. Resonant two-photon photoelectron imaging (R2P-PEI) via the vibrational levels of the DBS displays a sharp peak with a constant binding energy. This observation indicates vertical detachment from the vibrational levels of the DBS to the corresponding neutral levels with the conservation of the vibrational energy, suggesting that the highly diffuse electron in the DBS has little effect on the neutral core. The R2P-PEI spectra also exhibit two features at lower binding energies, which come from intersystem crossings from the DBS to two lower-lying valence-bound triplet excited states of bPh-. The current study discloses the first R2P-PEI spectra from vibrational excited states of a DBS and direct spectroscopic evidence of transitions from a DBS to valence-bound states of anions.
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Affiliation(s)
- Guo-Zhu Zhu
- Department of Chemistry , Brown University , Providence , Rhode Island 02912 , United States
| | - Ling Fung Cheung
- Department of Chemistry , Brown University , Providence , Rhode Island 02912 , United States
| | - Yuan Liu
- Department of Chemistry , Brown University , Providence , Rhode Island 02912 , United States
| | - Chen-Hui Qian
- Department of Chemistry , Brown University , Providence , Rhode Island 02912 , United States
| | - Lai-Sheng Wang
- Department of Chemistry , Brown University , Providence , Rhode Island 02912 , United States
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