Ring Opening upon Valence Shell Excitation in β-Butyrolactone: Experimental and Theoretical Methods
The valence-shell electronic state spectroscopy of β-butyrolactone (CH<sub>3</sub>CHCH<sub>2</sub>CO<sub>2</sub>) is comprehensively investigated by employing experimental and theoretical methods. We report a novel vacuum ultraviolet (VUV) absorption spectrum in t...
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| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2025-07-01
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| Series: | Molecules |
| Subjects: | |
| Online Access: | https://www.mdpi.com/1420-3049/30/15/3137 |
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| Summary: | The valence-shell electronic state spectroscopy of β-butyrolactone (CH<sub>3</sub>CHCH<sub>2</sub>CO<sub>2</sub>) is comprehensively investigated by employing experimental and theoretical methods. We report a novel vacuum ultraviolet (VUV) absorption spectrum in the photon wavelength range from 115 to 320 nm (3.9–10.8 eV), together with ab initio quantum chemical calculations at the time-dependent density functional (TD-DFT) level of theory. The dominant electronic excitations are assigned to mixed valence-Rydberg and Rydberg transitions. The fine structure in the CH<sub>3</sub>CHCH<sub>2</sub>CO<sub>2</sub> photoabsorption spectrum has been assigned to C=O stretching, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mrow><mi>v</mi></mrow><mrow><mn>7</mn></mrow><mrow><mo>′</mo></mrow></msubsup><mfenced separators="|"><mrow><mi>a</mi></mrow></mfenced></mrow></semantics></math></inline-formula>, CH<sub>2</sub> wagging, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mrow><mi>v</mi></mrow><mrow><mn>14</mn></mrow><mrow><mo>′</mo></mrow></msubsup><mfenced separators="|"><mrow><mi>a</mi></mrow></mfenced></mrow></semantics></math></inline-formula>, C–O stretching, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mrow><mi>v</mi></mrow><mrow><mn>22</mn></mrow><mrow><mo>′</mo></mrow></msubsup><mfenced separators="|"><mrow><mi>a</mi></mrow></mfenced></mrow></semantics></math></inline-formula>, and C=O bending, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mrow><mi>v</mi></mrow><mrow><mn>26</mn></mrow><mrow><mo>′</mo></mrow></msubsup><mfenced separators="|"><mrow><mi>a</mi></mrow></mfenced></mrow></semantics></math></inline-formula> modes. Photolysis lifetimes in the Earth’s atmosphere from 0 km up to 50 km altitude have been estimated, showing to be a non-relevant sink mechanism compared to reactions with the <sup>•</sup>OH radical. The nuclear dynamics along the C=O and C–C–C coordinates have been investigated at the TD-DFT level of theory, where, upon electronic excitation, the potential energy curves show important carbonyl bond breaking and ring opening, respectively. Within such an intricate molecular landscape, the higher-lying excited electronic states may keep their original Rydberg character or may undergo Rydberg-to-valence conversion, with vibronic coupling as an important mechanism contributing to the spectrum. |
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| ISSN: | 1420-3049 |