High-resolution rovibrational spectroscopy of trans-formic acid in the v1 OH stretching fundamental: Dark state coupling and evidence for charge delocalization dynamics
IF 1.4 4区 物理与天体物理Q4 PHYSICS, ATOMIC, MOLECULAR & CHEMICAL
{"title":"High-resolution rovibrational spectroscopy of trans-formic acid in the v1 OH stretching fundamental: Dark state coupling and evidence for charge delocalization dynamics","authors":"Ya-Chu Chan , David J. Nesbitt","doi":"10.1016/j.jms.2023.111743","DOIUrl":null,"url":null,"abstract":"<div><p><span>High-resolution infrared (IR) reduced-Doppler absorption spectra of jet-cooled gas phase </span><em>trans</em>-formic acid in the <em>v</em><sub>1</sub> OH stretching fundamental region are reported for the first time, obtained by supersonically expanding <em>trans-</em>formic acid/Ar mixtures through a slit jet nozzle source and rotationally cooling to T<sub>rot</sub><span> ≈ 10.9(5) K, with absorption signals recorded by high-resolution difference-frequency IR absorption spectroscopy. Two </span><em>a</em>/<em>b</em>-type rovibrational bands of comparable intensity, one ∼10-fold weaker <em>b</em>-type band, and one ∼6-fold weaker <em>a</em>-type band are observed, with vibrational band origins at 3570.493(5), 3566.793(5), 3560.032(9), and 3534.6869(2) cm<sup>−1</sup>, respectively. Based on previous Raman jet spectroscopic work by Nejad and Sibert [A. Nejad, E.L. Sibert III, The Raman jet spectrum of <em>trans</em>-formic acid and its deuterated isotopologs: Combining theory and experiment to extend the vibrational database, J. Chem. Phys. 154(6) (2021) 064301.], these four rovibrational bands have been assigned to <em>v</em><sub>1</sub>, (<em>v</em><sub>2</sub> + <em>v</em><sub>7</sub>), (<em>v</em><sub>6</sub> + 2<em>v</em><sub>7</sub> + 2<em>v</em><sub>9</sub>), and 2<em>v</em><sub>3</sub>, respectively. Specifically, two of the three upper dark states (2<sup>1</sup>7<sup>1</sup> (<em>a</em>′) and 6<sup>1</sup>7<sup>2</sup>9<sup>2</sup> (<em>a</em>′)) are close enough to the “bright” 1<sup>1</sup> (<em>a</em>′) state to facilitate strong anharmonic resonance interactions, which results in intensity mixing into the two zero-order bands that would otherwise be “dark”. Furthermore, our high-resolution spectral analysis reveals that there are local rotational crossings between these zero-order 1<sup>1</sup> and 2<sup>1</sup>7<sup>1</sup> states resulting in extra lines (i.e., some upper levels in the nominally <em>v</em><sub>1</sub> band have majority zero-order 2<sup>1</sup>7<sup>1</sup> state character). This motivates development of a 3 coupled state (1<sup>1</sup>, 2<sup>1</sup>7<sup>1</sup>, and 6<sup>1</sup>7<sup>2</sup>9<sup>2</sup>) picture to aid in the spectral analysis, which is able to match all 3 observed band origins and relative band intensities, as well as indicate the necessity of multistate (> 2) coupling. Though limited by range of <em>J</em> and <em>K</em><sub>a</sub> levels (<em>J'</em> ≤ 9 and <em>K</em><sub><em>a</em></sub><em>'</em><span> ≤ 3) populated at supersonic<span> jet temperatures, this work offers first precision spectroscopic analysis of </span></span><em>trans</em>-formic acid in the <em>v</em><sub>1</sub><span><span> OH stretch region, which should aid in assignment of the more complete yet highly congested room temperature </span>FTIR spectra [D. Hurtmans, F. Herregodts, M. Herman, J. Liévin, A. Campargue, A. Garnache, A. Kachanov, Spectroscopic and ab initio investigation of the ν</span><sub>OH</sub> overtone excitation in <em>trans</em>-formic acid, J. Chem. Phys. 113(4) (2000) 1535–1545.]. Finally, and in sharp contrast to the spectral complexity in the three predominantly <em>b</em>-type bands, the lone <em>a</em>-type 2<em>v</em><sub>3</sub> rovibrational band at 3534.6869(2) cm<sup>−1</sup> is well described by a simple, rigid asymmetric top Hamiltonian.</p></div>","PeriodicalId":16367,"journal":{"name":"Journal of Molecular Spectroscopy","volume":null,"pages":null},"PeriodicalIF":1.4000,"publicationDate":"2023-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Molecular Spectroscopy","FirstCategoryId":"101","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0022285223000085","RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"PHYSICS, ATOMIC, MOLECULAR & CHEMICAL","Score":null,"Total":0}
引用次数: 0
Abstract
High-resolution infrared (IR) reduced-Doppler absorption spectra of jet-cooled gas phase trans-formic acid in the v1 OH stretching fundamental region are reported for the first time, obtained by supersonically expanding trans-formic acid/Ar mixtures through a slit jet nozzle source and rotationally cooling to Trot ≈ 10.9(5) K, with absorption signals recorded by high-resolution difference-frequency IR absorption spectroscopy. Two a/b-type rovibrational bands of comparable intensity, one ∼10-fold weaker b-type band, and one ∼6-fold weaker a-type band are observed, with vibrational band origins at 3570.493(5), 3566.793(5), 3560.032(9), and 3534.6869(2) cm−1, respectively. Based on previous Raman jet spectroscopic work by Nejad and Sibert [A. Nejad, E.L. Sibert III, The Raman jet spectrum of trans-formic acid and its deuterated isotopologs: Combining theory and experiment to extend the vibrational database, J. Chem. Phys. 154(6) (2021) 064301.], these four rovibrational bands have been assigned to v1, (v2 + v7), (v6 + 2v7 + 2v9), and 2v3, respectively. Specifically, two of the three upper dark states (2171 (a′) and 617292 (a′)) are close enough to the “bright” 11 (a′) state to facilitate strong anharmonic resonance interactions, which results in intensity mixing into the two zero-order bands that would otherwise be “dark”. Furthermore, our high-resolution spectral analysis reveals that there are local rotational crossings between these zero-order 11 and 2171 states resulting in extra lines (i.e., some upper levels in the nominally v1 band have majority zero-order 2171 state character). This motivates development of a 3 coupled state (11, 2171, and 617292) picture to aid in the spectral analysis, which is able to match all 3 observed band origins and relative band intensities, as well as indicate the necessity of multistate (> 2) coupling. Though limited by range of J and Ka levels (J' ≤ 9 and Ka' ≤ 3) populated at supersonic jet temperatures, this work offers first precision spectroscopic analysis of trans-formic acid in the v1 OH stretch region, which should aid in assignment of the more complete yet highly congested room temperature FTIR spectra [D. Hurtmans, F. Herregodts, M. Herman, J. Liévin, A. Campargue, A. Garnache, A. Kachanov, Spectroscopic and ab initio investigation of the νOH overtone excitation in trans-formic acid, J. Chem. Phys. 113(4) (2000) 1535–1545.]. Finally, and in sharp contrast to the spectral complexity in the three predominantly b-type bands, the lone a-type 2v3 rovibrational band at 3534.6869(2) cm−1 is well described by a simple, rigid asymmetric top Hamiltonian.
期刊介绍:
The Journal of Molecular Spectroscopy presents experimental and theoretical articles on all subjects relevant to molecular spectroscopy and its modern applications. An international medium for the publication of some of the most significant research in the field, the Journal of Molecular Spectroscopy is an invaluable resource for astrophysicists, chemists, physicists, engineers, and others involved in molecular spectroscopy research and practice.