Asymmetric-top molecules containing one methyl-like internal rotor: Methods and codes for fitting and predicting spectra

Kleiner, Isabelle

doi:10.1016/j.jms.2009.12.011

Cited by 122 publications

(72 citation statements)

References 86 publications

(186 reference statements)

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“…Nonetheless, Kleiner reports that the barrier and structural parameters determined with XIAM fall within a few percent of the corresponding values obtained using the fitting program BELGI. 18 The ab initio rotational constants for these rigid ring systems were very close to the experimental values and provided an excellent starting point for assigning the measured spectra. The experimental A rotational constants were found to be within 2% of the values calculated at the MP2/6-311++G(d,p) level; B and C rotational constants were within 1% of the calculated values.…”

Section: ■ Discussionsupporting

confidence: 63%

Probing the Electronic Environment of Methylindoles using Internal Rotation and ¹⁴N Nuclear Quadrupole Coupling

Gurusinghe

Tubergen

2016

J. Phys. Chem. A

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High-resolution rotational spectra were recorded in the 10.5-21.0 GHz frequency range for seven singly methylated indoles. (14)N nuclear quadrupole hyperfine structure and spectral splittings arising from tunneling along the internal rotation of the methyl group were resolved for all indole species. The nuclear quadrupole coupling constants were used to characterize the electronic environment of the nitrogen atom, and the program XIAM was used to fit the barrier to internal rotation to the measured transition frequencies. The best fit barriers were found to be 277.1(2), 374.32(4), 414.(5), 331.6(2), 126.8675(15), 121.413(4), and 426(3) cm(-1) for 1-methylindole through 7-methylindole, respectively. The fitted barriers were found to be in good agreement with barriers calculated at the ωB97XD/6-311++G(d,p) level. The complete set of experimental barriers is compared to theoretical investigations of the origins of methyl torsional barriers and confirms that the magnitude of these barriers is an overall effect of individual hyperconjugative and structural interactions of many bonding/antibonding orbitals.

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Section: ■ Discussionsupporting

confidence: 63%

Probing the Electronic Environment of Methylindoles using Internal Rotation and ¹⁴N Nuclear Quadrupole Coupling

Gurusinghe

Tubergen

2016

J. Phys. Chem. A

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“…49−51, 44 The XIAM computer code 52 was used for these calculations. The periodicity of the potential energy function arising from the internal rotation was assumed to be 120°, as expected from the CH 3 group.…”

Section: ■ Resultsmentioning

confidence: 99%

Conformational Flexibility of Mephenesin

et al. 2014

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The mephenesin molecule (3-(2-methylphenoxy)propane-1,2-diol) serves as a test bank to explore several structural and dynamical issues, such as conformational flexibility, the orientation of the carbon linear chain relative to the benzene plane, or the effect of substituent position on the rotational barrier of a methyl group. The molecule has been studied by rotational spectroscopy in the 4-18 GHz frequency range by Fourier-transform methods in a supersonic expansion. The experiment has been backed by a previous conformational search plus optimization of the lowest energy structures by ab initio and density functional quantum calculations. The three lowest-lying conformers that can interconvert to each other by simple bond rotations have been detected in the jet. Rotational parameters for all structures have been obtained, and methyl torsional barriers have been determined for the two lowest-lying rotamers. The lowest-lying structure of mephenesin is highly planar, with all carbon atoms lying nearly in the benzene ring plane, and is stabilized by the formation of cooperative intramolecular hydrogen bonding. An estimation of the relative abundance of the detected conformers indicates that the energetically most stable conformer will have an abundance near 80% at temperatures relevant for biological activity.

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“…The BELGI-C s -hyperfine code was then used, which is a slightly modified version of the BELGI-C 1 -hyperfine code allowing for treatment of internal rotation effects with hyperfine structure for molecules with ap lanar frame. [16,26] The code uses the "Rho-Axis-method" (RAM) to minimise the torsion-rotation coupling in an effective Hamiltonian. [27] Like in BELGI-C 1 -hyperfine, the present code deals with the effect of the weak NQC using ap erturbation approachs imilar to that used for acetamide, [15] aC smolecule with one methyl internal rotor.…”

Section: Jet-cooled Mw Spectrum Analysismentioning

confidence: 99%

“…Unit BRAM ÀARAM with D ab the "Coriolis-like" operator coefficient corresponding to the off-diagonal elemento ft he inertial tensor in RAM system. [26] [e] The BELGI-C s -hyperfinev alue of the angle ff(i,a)i so btained from Equation (10) www.chemphyschem.org also transformed into the RAM system.Internal rotation parameters V 3 , F and 1 were estimated from the calculated molecular structure at equilibrium (see Section4.2 and Table S1 with all the calculated parameters used as starting values for the fit).…”

Section: Jet-cooled Mw Spectrum Analysismentioning

confidence: 99%

“…Whereas the first diagonalisation of the Hamiltonian is performed on as ize-limited matrix (21 21) withouta ny dependence on J,t he second diagonalisation (yielding the rotation, centrifugal distortion, andr otation-torsion coupling terms) is performed on a9 (2J + 1) 9(2J + 1) dimensional matrix (see Ref. [26] and references therein).…”

Section: Limitations Of the Modelmentioning

confidence: 99%

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

et al. 2018

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The monitoring of gas-phase mononitrotoluenes is crucial for defence, civil security and environmental interests because they are used as taggant for TNT detection and in the manufacturing of industrial compounds such as dyestuffs. In this study, we have succeeded to measure and analyse at high-resolution a room temperature rotationally resolved millimetre-wave spectrum of meta-nitrotoluene (3-NT). Experimental and theoretical difficulties have been overcome, in particular, those related to the low vapour pressure of 3-NT and to the presence of a CH internal rotation in an almost free rotation regime (V =6.7659(24) cm ). Rotational spectra have been recorded in the microwave and millimetre-wave ranges using a supersonic jet Fourier Transform microwave spectrometer (T <10 K) and a millimetre-wave frequency multiplication chain (T=293 K), respectively. Spectral analysis of pure rotation lines in the vibrational ground state and in the first torsional excited state supported by quantum chemistry calculations permits the rotational energy of the molecule, the hyperfine structure due to the N nucleus, and the internal rotation of the methyl group to be characterised. A line list is provided for future in situ detection.

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Asymmetric-top molecules containing one methyl-like internal rotor: Methods and codes for fitting and predicting spectra

Cited by 122 publications

References 86 publications

Probing the Electronic Environment of Methylindoles using Internal Rotation and ¹⁴N Nuclear Quadrupole Coupling

Probing the Electronic Environment of Methylindoles using Internal Rotation and ¹⁴N Nuclear Quadrupole Coupling

Conformational Flexibility of Mephenesin

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

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Asymmetric-top molecules containing one methyl-like internal rotor: Methods and codes for fitting and predicting spectra

Cited by 122 publications

References 86 publications

Probing the Electronic Environment of Methylindoles using Internal Rotation and 14N Nuclear Quadrupole Coupling

Probing the Electronic Environment of Methylindoles using Internal Rotation and 14N Nuclear Quadrupole Coupling

Conformational Flexibility of Mephenesin

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

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Probing the Electronic Environment of Methylindoles using Internal Rotation and ¹⁴N Nuclear Quadrupole Coupling

Probing the Electronic Environment of Methylindoles using Internal Rotation and ¹⁴N Nuclear Quadrupole Coupling