Cis-trans isomerization in the S[subscript 1] state of acetylene: Identification of cis-well vibrational levels
A systematic analysis of the S[subscript 1]-trans ([bar-over A][superscript 1]A[subscript u]) state of acetylene, using IR-UV double resonance along with one-photon fluorescence excitation spectra, has allowed assignment of at least part of every single vibrational state or polyad up to a vibrationa...
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| Format: | Article |
| Language: | en_US |
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American Institute of Physics (AIP)
2012
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| Online Access: | http://hdl.handle.net/1721.1/73983 https://orcid.org/0000-0002-7609-4205 |
| _version_ | 1811087216093429760 |
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| author | Merer, Anthony J. Steeves, Adam H. Baraban, Joshua H. Bechtel, Hans A. Field, Robert W. |
| author2 | Massachusetts Institute of Technology. Department of Chemistry |
| author_facet | Massachusetts Institute of Technology. Department of Chemistry Merer, Anthony J. Steeves, Adam H. Baraban, Joshua H. Bechtel, Hans A. Field, Robert W. |
| author_sort | Merer, Anthony J. |
| collection | MIT |
| description | A systematic analysis of the S[subscript 1]-trans ([bar-over A][superscript 1]A[subscript u]) state of acetylene, using IR-UV double resonance along with one-photon fluorescence excitation spectra, has allowed assignment of at least part of every single vibrational state or polyad up to a vibrational energy of 4200 cm[superscript –1]. Four observed vibrational levels remain unassigned, for which no place can be found in the level structure of the trans-well. The most prominent of these lies at 46 175 cm[superscript –1]. Its [superscript 13]C isotope shift, exceptionally long radiative lifetime, unexpected rotational selection rules, and lack of significant Zeeman effect, combined with the fact that no other singlet electronic states are expected at this energy, indicate that it is a vibrational level of the S[subscript 1-]cis isomer ([bar-over A][superscript 1]A[subscript 2]). Guided by ab initio calculations [J. H. Baraban, A. R. Beck, A. H. Steeves, J. F. Stanton, and R. W. Field, J. Chem. Phys. 134, 244311 (2011)]10.1063/1.3570823 of the cis-well vibrational frequencies, the vibrational assignments of these four levels can be established from their vibrational symmetries together with the [superscript 13]C isotope shift of the 46 175 cm[superscript −1] level (assigned here as cis-3[superscript 1]6[superscript 1]). The S[subscript 1]-cis zero-point level is deduced to lie near 44 900 cm[superscript −1], and the ν[subscript 6] vibrational frequency of the S[subscript 1]-cis well is found to be roughly 565 cm[superscript −1]; these values are in remarkably good agreement with the results of recent ab initio calculations. The 46 175 cm[superscript −1] vibrational level is found to have a 3.9 cm[superscript −1] staggering of its K-rotational structure as a result of quantum mechanical tunneling through the isomerization barrier. Such tunneling does not give rise to ammonia-type inversion doubling, because the cis and trans isomers are not equivalent; instead the odd-K rotational levels of a given vibrational level are systematically shifted relative to the even-K rotational levels, leading to a staggering of the K-structure. These various observations represent the first definite assignment of an isomer of acetylene that was previously thought to be unobservable, as well as the first high resolution spectroscopic results describing cis-trans isomerization. |
| first_indexed | 2024-09-23T13:41:55Z |
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| id | mit-1721.1/73983 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T13:41:55Z |
| publishDate | 2012 |
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| spelling | mit-1721.1/739832022-09-28T15:35:28Z Cis-trans isomerization in the S[subscript 1] state of acetylene: Identification of cis-well vibrational levels Merer, Anthony J. Steeves, Adam H. Baraban, Joshua H. Bechtel, Hans A. Field, Robert W. Massachusetts Institute of Technology. Department of Chemistry Field, Robert W. Steeves, Adam H. Baraban, Joshua H. Bechtel, Hans A. Field, Robert W. A systematic analysis of the S[subscript 1]-trans ([bar-over A][superscript 1]A[subscript u]) state of acetylene, using IR-UV double resonance along with one-photon fluorescence excitation spectra, has allowed assignment of at least part of every single vibrational state or polyad up to a vibrational energy of 4200 cm[superscript –1]. Four observed vibrational levels remain unassigned, for which no place can be found in the level structure of the trans-well. The most prominent of these lies at 46 175 cm[superscript –1]. Its [superscript 13]C isotope shift, exceptionally long radiative lifetime, unexpected rotational selection rules, and lack of significant Zeeman effect, combined with the fact that no other singlet electronic states are expected at this energy, indicate that it is a vibrational level of the S[subscript 1-]cis isomer ([bar-over A][superscript 1]A[subscript 2]). Guided by ab initio calculations [J. H. Baraban, A. R. Beck, A. H. Steeves, J. F. Stanton, and R. W. Field, J. Chem. Phys. 134, 244311 (2011)]10.1063/1.3570823 of the cis-well vibrational frequencies, the vibrational assignments of these four levels can be established from their vibrational symmetries together with the [superscript 13]C isotope shift of the 46 175 cm[superscript −1] level (assigned here as cis-3[superscript 1]6[superscript 1]). The S[subscript 1]-cis zero-point level is deduced to lie near 44 900 cm[superscript −1], and the ν[subscript 6] vibrational frequency of the S[subscript 1]-cis well is found to be roughly 565 cm[superscript −1]; these values are in remarkably good agreement with the results of recent ab initio calculations. The 46 175 cm[superscript −1] vibrational level is found to have a 3.9 cm[superscript −1] staggering of its K-rotational structure as a result of quantum mechanical tunneling through the isomerization barrier. Such tunneling does not give rise to ammonia-type inversion doubling, because the cis and trans isomers are not equivalent; instead the odd-K rotational levels of a given vibrational level are systematically shifted relative to the even-K rotational levels, leading to a staggering of the K-structure. These various observations represent the first definite assignment of an isomer of acetylene that was previously thought to be unobservable, as well as the first high resolution spectroscopic results describing cis-trans isomerization. United States. Dept. of Energy (Grant DE-FG0287ER13671) National Science Foundation (U.S.). Graduate Research Fellowship Program 2012-10-15T18:09:49Z 2012-10-15T18:09:49Z 2011-06 2011-03 Article http://purl.org/eprint/type/JournalArticle 0021-9606 1089-7690 http://hdl.handle.net/1721.1/73983 Merer, Anthony J. et al. “Cis-trans Isomerization in the S1 State of Acetylene: Identification of Cis-well Vibrational Levels.” The Journal of Chemical Physics 134.24 (2011): 244310. © 2011 American Institute of Physics https://orcid.org/0000-0002-7609-4205 en_US http://dx.doi.org/10.1063/1.3599091 Journal of Chemical Physics Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf American Institute of Physics (AIP) Prof. Field via Erja Kajosalo |
| spellingShingle | Merer, Anthony J. Steeves, Adam H. Baraban, Joshua H. Bechtel, Hans A. Field, Robert W. Cis-trans isomerization in the S[subscript 1] state of acetylene: Identification of cis-well vibrational levels |
| title | Cis-trans isomerization in the S[subscript 1] state of acetylene: Identification of cis-well vibrational levels |
| title_full | Cis-trans isomerization in the S[subscript 1] state of acetylene: Identification of cis-well vibrational levels |
| title_fullStr | Cis-trans isomerization in the S[subscript 1] state of acetylene: Identification of cis-well vibrational levels |
| title_full_unstemmed | Cis-trans isomerization in the S[subscript 1] state of acetylene: Identification of cis-well vibrational levels |
| title_short | Cis-trans isomerization in the S[subscript 1] state of acetylene: Identification of cis-well vibrational levels |
| title_sort | cis trans isomerization in the s subscript 1 state of acetylene identification of cis well vibrational levels |
| url | http://hdl.handle.net/1721.1/73983 https://orcid.org/0000-0002-7609-4205 |
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