Cyclohexane Vibronic States: A Combined VUV Spectroscopy and Theoretical Study
In this work, we provide results from a joint experimental and theoretical study of the vibronic features of cyclohexane (C<sub>6</sub>H<sub>12</sub>) in the photon energy range of 6.8–10.8 eV (182–115 nm). The high-resolution vacuum ultraviolet (VUV) photoabsorption measurem...
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| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2025-03-01
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| Series: | Molecules |
| Subjects: | |
| Online Access: | https://www.mdpi.com/1420-3049/30/7/1493 |
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| Summary: | In this work, we provide results from a joint experimental and theoretical study of the vibronic features of cyclohexane (C<sub>6</sub>H<sub>12</sub>) in the photon energy range of 6.8–10.8 eV (182–115 nm). The high-resolution vacuum ultraviolet (VUV) photoabsorption measurements, together with quantum chemical calculations at the time-dependent density functional theory (TDDFT) level, have helped to assign the major electronic excitations to mixed valence–Rydberg and Rydberg transitions. The C<sub>6</sub>H<sub>12</sub> photoabsorption spectrum shows fine structure which has been assigned to CH<sub>2</sub> scissoring, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mi>v</mi><mn>3</mn><mo>′</mo></msubsup><mfenced><mrow><msub><mi>a</mi><mrow><mn>1</mn><mi>g</mi></mrow></msub></mrow></mfenced></mrow></semantics></math></inline-formula>, CH<sub>2</sub> rocking, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mi>v</mi><mn>4</mn><mo>′</mo></msubsup><mfenced><mrow><msub><mi>a</mi><mrow><mn>1</mn><mi>g</mi></mrow></msub></mrow></mfenced></mrow></semantics></math></inline-formula>, C–C stretching, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mi>v</mi><mn>5</mn><mo>′</mo></msubsup><mfenced><mrow><msub><mi>a</mi><mrow><mn>1</mn><mi>g</mi></mrow></msub></mrow></mfenced></mrow></semantics></math></inline-formula>, and CCC bending/CC torsion, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mi>v</mi><mrow><mn>24</mn></mrow><mo>′</mo></msubsup><mfenced><mrow><msub><mi>e</mi><mi>g</mi></msub></mrow></mfenced><mo>,</mo></mrow></semantics></math></inline-formula> modes. Molecular structure calculations at the DFT level for the neutral and cationic electronic ground-states have shown the relevant structural changes that are operative in the higher-lying electronic states. Photolysis lifetimes in the Earth’s atmosphere are shown to be irrelevant, while the main atmospheric sink mechanism is the reaction with the <sup>•</sup>OH radical. Potential energy curves have been obtained at the TDDFT level of theory, showing the relevance of interchange character mainly involving the CH<sub>2</sub> scissoring, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mi>v</mi><mn>3</mn><mo>′</mo></msubsup><mfenced><mrow><msub><mi>a</mi><mrow><mn>1</mn><mi>g</mi></mrow></msub></mrow></mfenced><mo>,</mo></mrow></semantics></math></inline-formula> and CH<sub>2</sub> rocking, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mi>v</mi><mn>4</mn><mo>′</mo></msubsup><mfenced><mrow><msub><mi>a</mi><mrow><mn>1</mn><mi>g</mi></mrow></msub></mrow></mfenced><mo>,</mo></mrow></semantics></math></inline-formula> modes, while Jahn–Teller distortion yields weak vibronic coupling involving the non-totally symmetric CCC bending/CC torsion, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mi>v</mi><mrow><mn>24</mn></mrow><mo>′</mo></msubsup><mfenced><mrow><msub><mi>e</mi><mi>g</mi></msub></mrow></mfenced><mo>,</mo></mrow></semantics></math></inline-formula> mode. |
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| ISSN: | 1420-3049 |