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Sturm F, Philipp LN, Flock M, Fischer I, Mitric R. The Electronic Structures of Azaphenanthrenes and Their Dimers. J Phys Chem A 2024; 128:1250-1259. [PMID: 38345912 DOI: 10.1021/acs.jpca.3c07740] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2024]
Abstract
Insertion of a nitrogen atom modifies the electronic structures and photochemistry of polycyclic aromatic hydrocarbons by introducing nπ* states into the molecules. To better understand the electronic structures of isolated polycyclic aromatic nitrogen-containing hydrocarbons (PANHs) and their dimers as well as the influence of the position of the nitrogen atom in the molecule, we investigate three different azaphenanthrenes, benzo[f]quinoline, benzo[h]quinoline, and phenanthridine, in a joint experimental and computational study. Experimentally, resonance-enhanced multiphoton ionization (REMPI) spectroscopy is applied to characterize the excited electronic states. The REMPI spectra of the azaphenanthrene monomers have a rather similar appearance, with origins between 3.645 and 3.670 eV for the 1ππ* ← S0 transition. In contrast to the phenanthrene parent, 2ππ* ← S0 is broad and unstructured even at the band origin. The experiments are accompanied by density functional theory computation, and vibrationally resolved spectra are simulated using a time-independent approach. The differences between phenanthrene and the azaphenanthrenes are assigned to perturbations due to the low-lying 1(nπ*) state, which accelerates nonradiative deactivation. For the dimers, it is found that two π-stacked isomers with two electronic transitions each contribute to the electronic spectrum, leading to overlapping bands that are difficult to assign.
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Affiliation(s)
- F Sturm
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, Würzburg D-97074, Germany
| | - L N Philipp
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, Würzburg D-97074, Germany
| | - M Flock
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, Würzburg D-97074, Germany
| | - I Fischer
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, Würzburg D-97074, Germany
| | - R Mitric
- Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, Würzburg D-97074, Germany
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Michon MA, Chmielniak P, Weber PM, Rose-Petruck C. Two-photon chemistry of tetrahydrofuran in clathrate hydrates. Phys Chem Chem Phys 2024; 26:2568-2579. [PMID: 38170862 DOI: 10.1039/d3cp02607h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
High-lying electronic states hold the potential for new and unusual photochemical reactions. However, for conventional single-photon excitation in the condensed phase, reaching these states is often not possible because the vacuum-ultraviolet (VUV) light required is competitively absorbed by the surrounding matrix rather than the molecule of interest. Here, this hurdle is overcome by leveraging nonresonant two-photon absorption (2PA) at 265 nm to achieve preferential photolysis of tetrahydrofuran (THF) trapped within a clathrate hydrate network at 77 K. Electron spin resonance (ESR) spectroscopy enables direct observation and identification of otherwise short-lived organic radicals stabilized by the clathrate cages, providing clues into the rapid dynamics that immediately follow photoexcitation. 2PA induces extensive fragmentation of enclathrated THF yielding 1-alkyl, acyl, allyl and methyl radicals-a stark departure from the reactive motifs commonly reported in γ-irradiated hydrates. We speculate on the undetected transient dynamics and explore the potential role of trapped electrons generated from water and THF. This demonstration of nonresonant two-photon chemistry presents an alternative approach to targeted condensed phase photochemistry in the VUV energy range.
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Affiliation(s)
- Michael A Michon
- Department of Chemistry, Brown University, Providence, 02912, Rhode Island, USA.
| | - Pawel Chmielniak
- Department of Chemistry, Brown University, Providence, 02912, Rhode Island, USA.
| | - Peter M Weber
- Department of Chemistry, Brown University, Providence, 02912, Rhode Island, USA.
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Fundamental Limits on Spatial Resolution in Ultrafast X-ray Diffraction. APPLIED SCIENCES-BASEL 2017. [DOI: 10.3390/app7060534] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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Minitti MP, Zhang Y, Rosenberg M, Brogaard RY, Deb S, Sølling TI, Weber PM. Far-UV photochemical bond cleavage of n-amyl nitrite: bypassing a repulsive surface. J Phys Chem A 2012; 116:810-9. [PMID: 22175717 DOI: 10.1021/jp209727g] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have investigated the deep-UV photoinduced, homolytic bond cleavage of amyl nitrite to form NO and pentoxy radicals. One-color multiphoton ionization with ultrashort laser pulses through the S(2) state resonance gives rise to photoelectron spectra that reflect ionization from the S(1) state. Time-resolved pump-probe photoionization measurements show that upon excitation at 207 nm, the generation of NO in the v = 2 state is delayed, with a rise time of 283 (16) fs. The time-resolved mass spectrum shows the NO to be expelled with a kinetic energy of 1.0 eV, which is consistent with dissociation on the S(1) state potential energy surface. Combined, these observations show that the first step of the dissociation reaction involves an internal conversion from the S(2) to the S(1) state, which is followed by the ejection of the NO radical on the predissociative S(1) state potential energy surface.
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Affiliation(s)
- Michael P Minitti
- SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
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Kuthirummal N, Rudakov FM, Evans CL, Weber PM. Spectroscopy and femtosecond dynamics of the ring opening reaction of 1,3-cyclohexadiene. J Chem Phys 2006; 125:133307. [PMID: 17029460 DOI: 10.1063/1.2345203] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The early stages of the ring opening reaction of 1,3-cyclohexadiene to form its isomer 1,3,5-hexatriene, upon excitation to the ultrashort-lived 1 1B2 state, were explored. A series of one-color two-photon ionization/photoelectron spectra reveal a prominent vibrational progression with a frequency of 1350 cm(-1), which is interpreted in a dynamical picture as resulting from the ultrafast wave packet dynamics associated with the ring opening reaction. Photoionization in two-color three-photon and one-color four-photon ionization schemes show an ionization pathway via the same ultrashort-lived 1 1B2 state, and in addition, a series of Rydberg states with quantum defects of 0.93, 0.76, and 0.15, respectively. Using those Rydberg states as probes for the reaction dynamics in a time-resolved pump-probe experiment provides a direct observation of the elusive 2 1A1 state that has been implicated as an intermediate step between the initially excited 1 1B2 state and the ground electronic state. The rise and decay times for the 2 1A1 state were found to be 55 and 84 fs, respectively.
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Affiliation(s)
- Narayanan Kuthirummal
- Department of Physics and Astronomy, College of Charleston, Charleston, South Carolina 29424, USA
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Minitti MP, Cardoza JD, Weber PM. Rydberg fingerprint spectroscopy of hot molecules: structural dispersion in flexible hydrocarbons. J Phys Chem A 2006; 110:10212-8. [PMID: 16928110 DOI: 10.1021/jp062539a] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
We explore how structural dispersion in flexible hydrocarbon chain molecules at very high temperatures is reflected in the photoionization spectra of Rydberg levels. The spectra of N,N-dimethylisopropanamine, N,N-dimethyl-1-butanamine, N,N-dimethyl-2-butanamine, N,N-dimethyl-3-hexanamine, and 1,4-dimethylpiperazine, taken at effective vibrational temperatures of 700-1000 K, show well-resolved features stemming from the 3p and 3s Rydberg states. The line shapes observed in molecules with internal rotation degrees of freedom show that multiple structures are populated. Following up on the discovery that low-lying Rydberg states provide sensitive fingerprints of molecular structures, this work supports Rydberg fingerprint spectroscopy as a tool to probe structural details of molecules in the presence of complex energy landscapes and at high vibrational temperatures. A simple model accounts for the sensitivity of Rydberg fingerprint spectroscopy to the molecular shape, as well as the relative insensitivity of the spectra toward vibrational excitation.
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Affiliation(s)
- Michael P Minitti
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA
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Schick CP, Weber PM. Ultrafast Dynamics in the Three-Photon, Double-Resonance Ionization of Phenol via the S2 Electronic State. J Phys Chem A 2001. [DOI: 10.1021/jp003304g] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Carolyn P. Schick
- Department of Chemistry, Brown University, Providence, Rhode Island 02912
| | - Peter M. Weber
- Department of Chemistry, Brown University, Providence, Rhode Island 02912
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Affiliation(s)
- Carolyn P. Schick
- Department of Chemistry, Brown University, Providence, Rhode Island 02912
| | - Peter M. Weber
- Department of Chemistry, Brown University, Providence, Rhode Island 02912
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Schick CP, Carpenter SD, Weber PM. Femtosecond Multiphoton Ionization Photoelectron Spectroscopy of the S2 State of Phenol. J Phys Chem A 1999. [DOI: 10.1021/jp992065y] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- Carolyn P. Schick
- Department of Chemistry and Department of Physics, Brown University, Providence, Rhode Island 02912
| | - Scott D. Carpenter
- Department of Chemistry and Department of Physics, Brown University, Providence, Rhode Island 02912
| | - Peter M. Weber
- Department of Chemistry and Department of Physics, Brown University, Providence, Rhode Island 02912
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