Electronic spectra of 2- and 3-tolunitrile in the gas phase. I. A study of methyl group internal rotation via rovibronically resolved spectroscopy

Abstract

Rotationally resolved fluorescence excitation spectra of the origin bands in the S1 ← S0 transition of 2-tolunitrile (2TN) and 3-tolunitrile (3TN) have been recorded in the collision-free environment of a molecular beam. Analyses of these data provide the rotational constants of each molecule and the potential energy curves governing the internal rotation of the attached methyl groups in both electronic states. 2TN exhibits much larger barriers along this coordinate than 3TN. Interestingly, the electronic transition dipole moment in both molecules is markedly influenced by the position of the attached methyl group rather than the position of the cyano group; possible reasons for this intriguing behavior are discussed.

Molecular force fields with gradient-domain machine learning: Construction and application to dynamics of small molecules with coupled cluster forces

“…n → σ * interactions [93], hyperconjugation, configuration dependent charge densities and Jahn-Teller effect [94]) that are not explicitly incorporated in conventional FFs, nor captured by less robust ML-FF frameworks, which limits the reliability and predictive power of the dynamics. This rigorous requirement is justified by the increasing demand of computationally inexpensive and highly accurate PESs to interpret and obtain further insights into state-of-the-art spectroscopic experimental results [94][95][96][97][98][99][100].…”

Towards the Detection of Explosive Taggants: Microwave and Millimetre‐Wave Gas‐Phase Spectroscopies of 3‐Nitrotoluene

“…Therefore, for ortho toluene derivatives, the V 3 barrier is significantly bigger, typically several hundreds of wavenumber units (e.g. ≈ 200 cm −1 for 2‐toluidine; ≈ 700 cm −1 for 2‐tolunitrile ) . In Table , V 3,6 barrier parameters determined in meta isomeric forms of mono‐substituted toluene derivatives are compared to our experimental results on 3‐NT.…”

“…In Table , V 3,6 barrier parameters determined in meta isomeric forms of mono‐substituted toluene derivatives are compared to our experimental results on 3‐NT. Depending on the molecule, the values of V 3 and V 6 have been fitted from MW rotational measurements or fitted and/or calculated from fluorescence excitation spectra . The value of the V 3 barrier of 3‐NT is interleaved between that of 3‐xylene and 3‐toluidine where the quasi free internal rotation is hindered by a methyl and an amino group, respectively.…”

“…[44] In Table 5, V 3,6 barrierparameters determinedi nmeta isomeric forms of mono-substituted toluene derivatives are comparedt oour experimental results on 3-NT.D epending on the molecule, the valueso fV 3 and V 6 have been fitted from MW rotational measurements [45][46][47] or fitted and/or calculated from fluorescenceexcitation spectra. [43,44,48] The value of the V 3 barrier of 3-NT is interleaved between that of 3-xylene and 3-toluidine where the quasi free internal rotationi sh indered by am ethyl anda n amino group, respectively.N evertheless, for such low barriers, the V 3 values are rather close andt heir level of accuracy and are therefore very important if we want to probe the CH 3 group molecular surrounding from the barrierh eight. With relative accuracies bettert han 1%,t he fitted barrier parameters of 3-NT reach al evel of accuracy significantly better than the others.…”

“…The second limitation of the model occurs for energy levels involving high J and K a quantum numbersw hen the wave functions begin to mix with each other,w hich leads to label [23,45] m-xylene-CH 3 4.49 (13) -FTMW spectroscopy [49] m-nitrotoluene -NO 2 6.7659(24) 0.02333 (22)t his work m-toluidine -NH 2 9 À10 fluorescence spectroscopy [48] m-tolunitrile -CN 13.58 (23) À13.68(560)r ovibronic spectroscopy [44] m-cresol-OD(trans) -OD 3.188(180)-rovibronic spectroscopy [43] m-cresol-OD(cis) -OD 21.341(52)-rovibronic spectroscopy [43]…”