Journal of Molecular Spectroscopy最新文献

{"title":"A new look at N2+ electronic transitions: An experimental and theoretical study","authors":"Laiz R. Ventura,&nbsp;Ramon S. da Silva,&nbsp;Jayr Amorim,&nbsp;Carlos E. Fellows","doi":"10.1016/j.jms.2024.111902","DOIUrl":"10.1016/j.jms.2024.111902","url":null,"abstract":"<div><p>Neutral and ionic N₂ species exhibit a rich spectrum as a result of the large density of couplings between states with different multiplicities. In this sense, spectra of the molecular ion N<span><math><msubsup><mrow></mrow><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math></span> are investigated combining Fourier transform spectroscopy and <em>ab initio</em> methods. We have reanalyzed the First Negative band System (B<span><math><mrow><msup><mrow></mrow><mrow><mn>2</mn></mrow></msup><msubsup><mrow><mi>Σ</mi></mrow><mrow><mi>u</mi></mrow><mrow><mo>+</mo></mrow></msubsup></mrow></math></span> <span><math><mo>→</mo></math></span> X<span><math><mrow><msup><mrow></mrow><mrow><mn>2</mn></mrow></msup><msubsup><mrow><mi>Σ</mi></mrow><mrow><mi>g</mi></mrow><mrow><mo>+</mo></mrow></msubsup></mrow></math></span>) including five bands not reported previously by Fourier spectroscopy. The spectra were recorded using a resolution of 0.6 cm⁻¹ and accuracy of 0.005 cm⁻¹. These results are then compared with new MRCI+Q/AV6Z calculations. For the first time, transition probabilities are computed for the previously observed 2<span><math><mrow><msup><mrow></mrow><mrow><mn>2</mn></mrow></msup><msub><mrow><mi>Π</mi></mrow><mrow><mi>g</mi></mrow></msub></mrow></math></span>-A<span><math><mrow><msup><mrow></mrow><mrow><mn>2</mn></mrow></msup><msub><mrow><mi>Π</mi></mrow><mrow><mi>u</mi></mrow></msub></mrow></math></span> band system. The 2<span><math><mrow><msup><mrow></mrow><mrow><mn>2</mn></mrow></msup><msub><mrow><mi>Π</mi></mrow><mrow><mi>g</mi></mrow></msub></mrow></math></span> state (<span><math><msub><mrow><mi>T</mi></mrow><mrow><mi>e</mi></mrow></msub></math></span> = 67,029 cm⁻¹) has a dissociation energy of 24,787 cm⁻¹ at <span><math><msub><mrow><mi>R</mi></mrow><mrow><mi>e</mi></mrow></msub></math></span> = 2.7332 a₀. The predicted lifetimes for the 2<span><math><mrow><msup><mrow></mrow><mrow><mn>2</mn></mrow></msup><msub><mrow><mi>Π</mi></mrow><mrow><mi>g</mi></mrow></msub></mrow></math></span>-A<span><math><mrow><msup><mrow></mrow><mrow><mn>2</mn></mrow></msup><msub><mrow><mi>Π</mi></mrow><mrow><mi>u</mi></mrow></msub></mrow></math></span> emissions are of the order of 170 ns. The calculated transition probabilities A(<span><math><msup><mrow><mi>v</mi></mrow><mrow><mo>′</mo></mrow></msup></math></span>=0, <span><math><msup><mrow><mi>v</mi></mrow><mrow><mo>′</mo><mo>′</mo></mrow></msup></math></span>=0) for the B<span><math><mrow><msup><mrow></mrow><mrow><mn>2</mn></mrow></msup><msubsup><mrow><mi>Σ</mi></mrow><mrow><mi>u</mi></mrow><mrow><mo>+</mo></mrow></msubsup></mrow></math></span>-X<span><math><mrow><msup><mrow></mrow><mrow><mn>2</mn></mrow></msup><msubsup><mrow><mi>Σ</mi></mrow><mrow><mi>g</mi></mrow><mrow><mo>+</mo></mrow></msubsup></mrow></math></span> and 2<span><math><mrow><msup><mrow></mrow><mrow><mn>2</mn></mrow></msup><msub><mrow><mi>Π</mi></mrow><mrow><mi>","PeriodicalId":16367,"journal":{"name":"Journal of Molecular Spectroscopy","volume":"401 ","pages":"Article 111902"},"PeriodicalIF":1.4,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140407162","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Predicting the rotational dependence of line broadening using machine learning","authors":"Elizabeth R. Guest,&nbsp;Jonathan Tennyson,&nbsp;Sergei N. Yurchenko","doi":"10.1016/j.jms.2024.111901","DOIUrl":"https://doi.org/10.1016/j.jms.2024.111901","url":null,"abstract":"<div><p>Correct pressure broadening is essential for modelling radiative transfer in atmospheres, however data are lacking for the many exotic molecules expected in exoplanetary atmospheres. Here we explore modern machine learning methods to mass produce pressure broadening parameters for a large number of molecules in the ExoMol data base. To this end, state-of-the-art machine learning models are used to fit to existing, empirical air-broadening data from the HITRAN database. A computationally cheap method for large-scale production of pressure broadening parameters is developed, which is shown to be reasonably (69%) accurate for unseen active molecules. This method has been used to augment the previously insufficient ExoMol line broadening diet, providing air-broadening data for all ExoMol molecules, so that the ExoMol database has a full and more accurate treatment of line broadening. Suggestions are made for improved air-broadening parameters for species present in atmospheric databases.</p></div>","PeriodicalId":16367,"journal":{"name":"Journal of Molecular Spectroscopy","volume":"401 ","pages":"Article 111901"},"PeriodicalIF":1.4,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0022285224000286/pdfft?md5=bb9e0d35ca6f02e39044595f28bd089d&pid=1-s2.0-S0022285224000286-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140180150","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Laboratory rotational spectroscopy of the magnesium-carbon chains MgC4H and MgC3N","authors":"P. Bryan Changala ,&nbsp;Nadav Genossar-Dan ,&nbsp;Joshua H. Baraban ,&nbsp;Michael C. McCarthy","doi":"10.1016/j.jms.2024.111904","DOIUrl":"https://doi.org/10.1016/j.jms.2024.111904","url":null,"abstract":"<div><p>Recent advances in circumstellar metal chemistry and laser-coolable molecules have spurred interest in the spectroscopy and electronic properties of alkaline earth metal-bearing polyatomic molecules. We report the microwave rotational spectra of two members of this important chemical family, the linear magnesium-carbon chains MgC<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span>H and MgC<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>N, detected with cavity Fourier transform microwave spectroscopy of a laser ablation-electric discharge expansion. The rotation, fine, and hyperfine parameters have been derived from the precise laboratory rest frequencies. These experimental results, combined with a theoretical quantum chemical analysis, confirm the recent identification of MgC<span><math><msub><mrow></mrow><mrow><mn>4</mn></mrow></msub></math></span>H and MgC<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>N in the circumstellar envelope of the evolved carbon-rich star IRC+10216. The spectroscopic data also provide insight into the structural and electronic properties that influence the metal-based optical cycling center in this unique class of laser-coolable polyatomics.</p></div>","PeriodicalId":16367,"journal":{"name":"Journal of Molecular Spectroscopy","volume":"401 ","pages":"Article 111904"},"PeriodicalIF":1.4,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140604833","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Measurements of infrared absorption cross-sections for n-C3F8, c-C4F8, n-C4F10, and n-C5F12 from 298 to 350 K","authors":"Muhammad Osama Ishtiak ,&nbsp;Orfeo Colebatch ,&nbsp;Karine Le Bris ,&nbsp;Paul J. Godin ,&nbsp;Kimberly Strong","doi":"10.1016/j.jms.2024.111900","DOIUrl":"10.1016/j.jms.2024.111900","url":null,"abstract":"<div><p>Perfluoro-n-propane, perfluorocyclobutane, perfluoro-n-butane, and perfluoro-n-pentane are non-ozone-depleting industrial alternatives to chlorofluorocarbons and hydrochlorofluorocarbons. However, these perfluoroalkanes have significant band strength in the atmospheric window from 800 to 1200 cm⁻¹. Coupled with their millennial-scale atmospheric lifetimes, they can lead to significant long-term global warming. Infrared spectra are required to quantify the climate impacts. This work provides a set of high-temperature infrared absorption cross-sections in the range 298–350 K at 0.1 cm⁻¹ resolution from 515 to 1500 cm⁻¹ for each compound. Our cross-sections generally agree with literature measurements except for perfluoro-n-pentane. We use density functional theory to calculate the absorption cross-sections from 0 to 515 cm⁻¹ using the B3LYP functional and several basis sets. The 6-31G(d,p) basis set provides the best results for linear perfluoroalkanes, while the def2-TZVP basis set provides the best results for cyclic perfluoroalkanes. Using experimental cross-sections, we calculate the radiative efficiency and global warming potential for each compound, utilizing the Pinnock curve from Shine and Myhre (2020) and atmospheric lifetimes from Hodnebrog et al. (2020). These quantities are found to be independent of temperature. The average 100-year global warming potential derived from all cross-sections is 9,610±1,260, 10,800±1,420, 10,100±1,330, and 9,380±1,230 for perfluoro-n-propane, perfluorocyclobutane, perfluoro-n-butane, and perfluoro-n-pentane, respectively. Combining the data in this work with our previous measurements reveals that the global warming potential for perfluoroalkanes with an increasing number of C<img>F bonds depends on the ratio of radiative efficiency to molecular weight.</p></div>","PeriodicalId":16367,"journal":{"name":"Journal of Molecular Spectroscopy","volume":"401 ","pages":"Article 111900"},"PeriodicalIF":1.4,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0022285224000274/pdfft?md5=1606f942c2fb317c06570494fb3fba8f&pid=1-s2.0-S0022285224000274-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140154167","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Vibrational spectroscopy of aniline cations and their H-loss cations in helium droplets","authors":"Arisa Iguchi ,&nbsp;Amandeep Singh ,&nbsp;Susumu Kuma ,&nbsp;Hajime Tanuma ,&nbsp;Toshiyuki Azuma","doi":"10.1016/j.jms.2024.111903","DOIUrl":"10.1016/j.jms.2024.111903","url":null,"abstract":"<div><p>We produced aniline cations (<span><math><mi>c</mi></math></span>–C₆H₅ <img>NH₂⁺) and their dehydro- (H-loss) cations inside helium droplets by electron ionization and observed their mass-selected vibrational spectra in the N<img>H stretching region. We observed vibrational bands at <em>m/q</em> = 93 which were identified as aniline cations. These bands showed only a few cm⁻¹ shifts from the symmetric and anti-symmetric N<img>H stretching bands for the amino (<img>NH₂) group in the gas phase. For the H-loss cation at mass <em>m/q</em> = 92, the agreement of the observed N<img>H band frequency with the result of DFT calculations suggests several candidate species, including a seven-membered ring structure, 4-monodehydro azepinylium (<span><math><mi>c</mi></math></span>–C₆NH₆⁺). A new reaction pathway to this cation was discussed by considering large excess energy in the ionization process.</p></div>","PeriodicalId":16367,"journal":{"name":"Journal of Molecular Spectroscopy","volume":"401 ","pages":"Article 111903"},"PeriodicalIF":1.4,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140398430","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Rotational detection of the silicon-carbon chains H2C3Si and HSiCCH","authors":"Michael C. McCarthy,&nbsp;P. Bryan Changala,&nbsp;P. Brandon Carroll","doi":"10.1016/j.jms.2024.111886","DOIUrl":"10.1016/j.jms.2024.111886","url":null,"abstract":"<div><p>The rotational spectra of two new silicon-bearing carbon chains, H₂C₃Si and HSiCCH have been detected by means of Fourier-transform microwave spectroscopy in a supersonic jet source equipped with an electrical discharge. On the basis of measurements between 10 and 42<!--> <!-->GHz, precise spectroscopic constants have been determined for both molecules. Along with H²⁹SiCCH and H³⁰SiCCH, which were detected in natural abundance, several other rare isotopic species of HSiCCH were observed using samples enriched in carbon-13 and D. From this isotopic data, a precise semi-experimental equilibrium structure was derived and compared with a re-evaluated semi-experimental equilibrium structure of the parent silylene SiH₂; the deuterium isotopic measurements also provide important clues as to the formation pathway of HSiCCH in our discharge. Because other small Si-bearing chains have been detected in the circumstellar envelope of the evolved carbon star IRC+10216, both chains may be of astronomical interest.</p></div>","PeriodicalId":16367,"journal":{"name":"Journal of Molecular Spectroscopy","volume":"400 ","pages":"Article 111886"},"PeriodicalIF":1.4,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139557719","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Diborane anharmonic vibrational frequencies and Intensities: Experiment and theory","authors":"Aaron I. Strom ,&nbsp;Ibrahim Muddasser ,&nbsp;Guntram Rauhut ,&nbsp;David T. Anderson","doi":"10.1016/j.jms.2024.111887","DOIUrl":"https://doi.org/10.1016/j.jms.2024.111887","url":null,"abstract":"<div><p>The vibrational dynamics of diborane have been extensively studied both theoretically and experimentally ever since the bridge structure of diborane was established in the 1950s. Numerous infrared and several Raman spectroscopic studies have followed in the ensuing years at ever increasing levels of spectral resolution. In parallel, <em>ab initio</em> computations of the underlying potential energy surface have progressed as well as the methods to calculate the anharmonic vibration dynamics beyond the double harmonic approximation. Nevertheless, even 70 years after the bridge structure of diborane was established, there are still significant discrepancies between experiment and theory for the fundamental vibrational frequencies of diborane. In this work we use parahydrogen (pH₂) matrix isolation infrared spectroscopy to characterize six fundamental vibrations of B₂H₆ and B₂D₆ and compare them with results from configuration-selective vibrational configuration interaction theory. The calculated frequencies and intensities are in very good agreement with the pH₂ matrix isolation spectra, even several combination bands are well reproduced. We believe that the reason discrepancies have existed for so long is related to the large amount of anharmonicity that is associated with the bridge BH stretching modes. However, the calculated frequencies and intensities reported here for the vibrational modes of all three boron isotopologues of B₂H₆ and B₂D₆ are within ± 2.00 cm⁻¹ and ± 1.44 cm⁻¹, respectively, of the experimental frequencies and therefore a refined vibrational assignment of diborane has been achieved.</p></div>","PeriodicalId":16367,"journal":{"name":"Journal of Molecular Spectroscopy","volume":"400 ","pages":"Article 111887"},"PeriodicalIF":1.4,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139733136","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Collision-broadening of vibration-inversion-rotation ammonia spectral lines in Q(J)-branch at 6.2 µm by cavity ring-down spectroscopy","authors":"Soumyadipta Chakraborty,&nbsp;Indrayani Patra,&nbsp;Ardhendu Pal,&nbsp;Manik Pradhan","doi":"10.1016/j.jms.2024.111891","DOIUrl":"https://doi.org/10.1016/j.jms.2024.111891","url":null,"abstract":"<div><p>In this experimental investigation, collision broadening effects on the Q(J)-branch vibration-inversion-rotation spectral lines of ammonia (NH₃) within the fundamental <span><math><msub><mi>ν</mi><mn>4</mn></msub></math></span> asymmetric bending vibrational band in the 6.2 µm mid-IR region are reported. A continuous-wave external-cavity quantum cascade laser coupled with a high-sensitive cavity ring-down spectrometer was employed to selectively probe 10 transitions in high-resolution, including few inversion doublets of gaseous NH₃. Pressure-broadening coefficients, <span><math><msub><mi>γ</mi><mrow><mi>N</mi><msub><mi>H</mi><mn>3</mn></msub><mo>-</mo><msub><mi>X</mi><mi>i</mi></msub></mrow></msub></math></span> (<span><math><msub><mi>X</mi><mi>i</mi></msub></math></span> = He, Ar, N_2, O_2, zero-air) in cm⁻¹ atm⁻¹, characterizing the collision interaction between NH₃ and various external perturbing gases, including helium, argon, nitrogen, oxygen, and zero-air, were determined at room temperature (296 K). Mean collision times and optical collision diameters of each collision partner were explored to gain deeper insight into the perturber-induced collision dynamics. This investigation elucidates the intricate intermolecular interactions and collision phenomena induced by various foreign perturbers with NH₃, with potential implications for future spectroscopic and atmospheric research of this polyatomic molecule.</p></div>","PeriodicalId":16367,"journal":{"name":"Journal of Molecular Spectroscopy","volume":"400 ","pages":"Article 111891"},"PeriodicalIF":1.4,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140031070","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Rotational and hyperfine structure in the A4Δ – X4Φ, B4Γ – X4Φ and C4Δ – X4Φ transitions of ruthenium monofluoride (RuF)","authors":"H. Zarringhalam ,&nbsp;D.W. Tokaryk ,&nbsp;A.G. Adam ,&nbsp;C. Linton","doi":"10.1016/j.jms.2024.111888","DOIUrl":"10.1016/j.jms.2024.111888","url":null,"abstract":"<div><p>Laser Induced Fluorescence (LIF) has been used to study the spectroscopy of ruthenium monofluoride (RuF) in the UNB laser-ablation molecular-jet apparatus. High-resolution spectra of three band systems have been obtained, with a linewidth (FWHM) of ∼0.004 cm⁻¹, in the near infrared (NIR), green and blue regions at ∼ 760 nm, 548 nm and 450 nm respectively. Electronic states have been assigned based on observation of first lines in the R and P branches and the excited states are labelled A, B and C in increasing energy order. Three transitions have been assigned to the green system as spin–orbit components, B⁴Γ_5.5 – X⁴Φ_4.5 and B⁴Γ_4.5 – X⁴Φ_3.5 of the (0,0) band, and B⁴Γ_5.5 – X⁴Φ_4.5 of the (1,1) band of the B – X system. The single NIR and blue bands were assigned as A⁴Δ_3.5 - X⁴Φ_4.5 (0,0) and C⁴Δ_3.5 - X⁴Φ_4.5 (0,0) respectively. Rotational structure of four individual isotopologues ⁹⁶RuF, ¹⁰⁰RuF, ¹⁰²RuF and ¹⁰⁴RuF was well resolved and used to examine the rotational and vibrational isotope effects. The rotational lines were doubled by hyperfine structure due to the nuclear spin I = ½ of fluorine. The hyperfine structure due to the nuclear spin I = 5/2 of ⁹⁹Ru and ¹⁰¹Ru was not resolved resulting in weak broadened ⁹⁹RuF and ¹⁰¹RuF lines that were overlapped by the stronger lines of the other isotopologues and could only be assigned in the C⁴Δ_3.5 - X⁴Φ_4.5 (0,0) band. The fluorine hyperfine structure was used to estimate the fraction of F 2sσ and 2pπ in the Ru-centered σ and π molecular orbitals.</p></div>","PeriodicalId":16367,"journal":{"name":"Journal of Molecular Spectroscopy","volume":"400 ","pages":"Article 111888"},"PeriodicalIF":1.4,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139890893","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reinvestigation of the Fourier transform microwave spectrum of N-ethylacetamide: Pseudo a-type transitions","authors":"Yoshiyuki Kawashima ,&nbsp;Nobuhiko Kuze ,&nbsp;Koichi M. T. Yamada ,&nbsp;Eizi Hirota","doi":"10.1016/j.jms.2023.111871","DOIUrl":"10.1016/j.jms.2023.111871","url":null,"abstract":"<div><p>We observed ten pseudo <em>a</em>-type transitions in the <em>E</em> state of <em>N</em>-ethylacetamide (NEAA) using a Fourier transform microwave spectrometer. We found triplets caused by the coupling between the two methyl groups for the observed pseudo <em>a</em>-type transitions. Also, we succeeded in observing similar triplets for the 5 <em>a</em>-type <em>Q</em>-branch transitions, 20 <em>b</em>-type and 7 <em>c</em>-type transitions of the <em>E</em> state of NEAA. These observed triplets allowed us to determinate the potential barrier <em>V</em>₃ to internal rotation of the ethyl-methyl group to be 1078 (12) cm⁻¹. In addition, though the observed intensities of the <em>c</em>-type transitions in the <em>A</em> state were weak, the <em>c</em>-type transition in the <em>E</em> state were observed to be as intense as the <em>b</em>-type transitions of the <em>E</em> state. We explained in this paper the abnormal intensities of the <em>c</em>-type transitions and pseudo <em>a</em>-type transitions in the <em>E</em> state of NEAA.</p></div>","PeriodicalId":16367,"journal":{"name":"Journal of Molecular Spectroscopy","volume":"400 ","pages":"Article 111871"},"PeriodicalIF":1.4,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138692987","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}