Molecular structures of gas-phase polyatomic molecules determined by spectroscopic methods

The structural and energetic properties of the H 2 S 2 molecule have been studied using density functional theory, second-order Møller-Plesset method, and coupled cluster theory with several basis sets. In order to extend previous work on intra-and intermolecular dynamics of the chirality changing modes for H 2 O 2 and its derivatives, our focus has been on the torsion around the S-S bond, along with an extensive characterization of the intermolecular potentials of H 2 S 2 with the rare gases ͑He, Ne, Ar, and Kr͒. Use is made of previously defined coordinates and expansion formulas for the potentials which allow for a faithful representation of geometrical and symmetry properties of these systems that involve the interaction of an atom with a floppy molecule. The potential energy surfaces obtained in this work are useful for classical and quantum mechanical simulations of molecular collisions responsible for chirality changing processes of possible interest in the modeling of prebiotic phenomena.

Section: A the H 2 S 2 Moleculecontrasting

confidence: 53%

A quantum chemical study of H2S2: Intramolecular torsional mode and intermolecular interactions with rare gases

Maciel

Barreto

Palazzetti

et al. 2008

“…͑1͒ Assume ground state geometries for the monomer structures ͑Harmony et al 41 ͒. ͑2͒ Angle COH of methanolϭ108.5°Ϸ109.5°, so assume a starting geometry of C, H, and the two lone pairs about oxygen that is tetrahedral.…”

Section: Structural Analysismentioning

confidence: 99%

Microwave rotation-tunneling spectroscopy of the water–methanol dimer: Direct structural proof for the strongest bound conformation

Stockman

Blake

Lovas

et al. 1997

Self Cite

O between 7 and 24 GHz using a Fourier-transform microwave spectrometer. Because CH 3 OH and H 2 O are capable of both accepting and donating hydrogen bonds, there exists some question as to which donor-acceptor pairing of the molecules is the lowest energy form. This question is further emphasized by the ambiguity and variety present in previous experimental and computational results. Transitions arising from the methyl torsional A state were assigned in each of the studied isotopomers, and for the A and E states in , where the errors correspond to 1 uncertainties-are consistent with either conformation, the fit of the structure to the rotational constants demonstrates unambiguously that the lower-energy conformation formed in supersonically cooled molecular beams corresponds to a water-donor, methanol-acceptor complex. The results and implications for future work are also discussed in terms of the permutation-inversion theory presented by Hougen and Ohashi ͓J. Mol. Spectros. 159, 363 ͑1993͔͒.

“…Within the 100 MHz scan, three transitions were observed within 15 MHz of each other. These signals are too close to be the 4 14 -3 13 transition, which is predicted to about 300 MHz lower in frequency. Similar scans at predicted transitions for 5 05 -4 04 and 4 14 -3 13 (as shown in Figure 2) were successfully used in the detection of this triad of signals.…”

Section: A 2-fluoro-benzoic Acid (I)mentioning

confidence: 99%

“…The resolution of rotational spectroscopy is usually sufficient to fully resolve the doublets to allow fitting a) Kukolich@u.arizona.edu of each state's rotational constants and, if enough transitions or if different dipole allowed transitions are measured, the ∆E(0 − -0 + ) (tunneling splitting) and F ab (axis-switching) term 11 can be determined. Pulsed beam microwave spectroscopy with a Fabry-Perot cavity offers excellent resolution and this allows resolved measurements for different conformers, 12 multiple isotopologues, 13 and various excited vibrational states. 14 Small changes in the geometries for the lowest two tunneling states cause subtle changes in the rotational constants that lead to distinct spectra.…”

Section: Introductionmentioning

confidence: 99%

Gas phase measurements of mono-fluoro-benzoic acids and the dimer of 3-fluoro-benzoic acid

Daly

Carey

Pejlovas

et al. 2015

The microwave spectrum of the mono-fluoro-benzoic acids, 2-fluoro-, 3-fluoro-, and 4-fluoro-benzoic acid have been measured in the frequency range of 4-14 GHz using a pulsed beam Fourier transform microwave spectrometer. Measured rotational transition lines were assigned and fit using a rigid rotor Hamiltonian. Assignments were made for 3 conformers of 2-fluorobenzoic acid, 2 conformers of 3-fluorobenzoic acid, and 1 conformer of 4-fluorobenzoic acid. Additionally, the gas phase homodimer of 3-fluorobenzoic acid was detected, and the spectra showed evidence of proton tunneling. Experimental rotational constants are A(0+) = 1151.8(5), B(0+) = 100.3(5), C(0+) = 87.64(3) MHz and A(0−) = 1152.2(5), B(0−) = 100.7(5), C(0−) = 88.85(3) MHz for the two ground vibrational states split by the proton tunneling motion. The tunneling splitting (ΔE) is approximately 560 MHz. This homodimer appears to be the largest carboxylic acid dimer observed with F-T microwave spectroscopy.