Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where Vinh Van is active.

Publication


Featured researches published by Vinh Van.


Journal of Physical Chemistry A | 2014

Methyl internal rotation in the microwave spectrum of vinyl acetate.

Ha Vinh Lam Nguyen; Atef Jabri; Vinh Van; Wolfgang Stahl

The rotational spectrum of vinyl acetate, CH3(CO)OCH═CH2, was measured using two molecular beam Fourier transform microwave spectrometers operating in the frequency range from 2 to 40 GHz. Large splittings up to 2 GHz occurred due to the internal rotation of the acetyl methyl group CH3CO with a V3 potential of 151.492(34) cm(-1), much larger than the barrier of approximately 100 cm(-1) often found in acetates. The torsional transitions were fitted using three different programs XIAM, ERHAM, and BELGI-Cs, whereby the rotational constants, centrifugal distortion constants, and the internal rotation parameters could be determined with very high accuracy. The experimental results were supported by quantum chemical calculations. For a conformational analysis, potential energy surfaces were calculated.


ChemPhysChem | 2016

Probing the Methyl Torsional Barriers of the E and Z Isomers of Butadienyl Acetate by Microwave Spectroscopy.

Atef Jabri; Vinh Van; Ha Vinh Lam Nguyen; Wolfgang Stahl; Isabelle Kleiner

The Fourier transform microwave spectra of the E and Z isomers of butadienyl acetate were measured in the frequency range from 2 to 26.5 GHz under molecular-jet conditions. The most stable conformer of each isomer, in which all heavy atoms are located in a symmetry plane, was identified after analyzing the spectrum by comparison with the results from quantum-chemical calculations. The barriers to internal rotation of the acetyl methyl group were found to be 149.1822(20) and 150.2128(48) cm(-1) for the E and Z isomers, respectively, which are similar to that of vinyl acetate. A comparison between two theoretical approaches treating internal rotation, the rho axis method and combined axis method, was also performed. The influence of the alkyl R chain on the methyl torsional barriers in CH3 -COOR acetates was explored.


Journal of Chemical Physics | 2014

The effects of two internal rotations in the microwave spectrum of ethyl methyl ketone.

Ha Vinh Lam Nguyen; Vinh Van; Wolfgang Stahl; Isabelle Kleiner

The rotational spectra of ethyl methyl ketone, CH3CH2COCH3, were measured in the microwave region from 2 to 40 GHz using two molecular beam Fourier transform microwave spectrometers. Splittings due to internal rotations of both, the acetyl methyl group -COCH3 and the ethyl methyl group CH3CH2CO-, could be completely resolved. All measured transitions were fitted using two different codes, XIAM and BELGI-Cs-2Tops. Molecular parameters like the rotational constants and the centrifugal distortion constants were determined with very high accuracy. The barrier to internal rotation of the acetyl methyl group was fitted to 181.502(98) cm(-1), much lower than the value of 763.87(65) cm(-1) found for the ethyl methyl group. The splittings in the spectrum due to internal rotation of the acetyl methyl group are accordingly much larger, up to 1.2 GHz, whereas for the ethyl methyl group only splittings from a few hundreds of kHz up to 4 MHz were observed.


ChemPhysChem | 2016

The Structure and Torsional Dynamics of Two Methyl Groups in 2-Acetyl-5-methylfuran as Observed by Microwave Spectroscopy.

Vinh Van; Wolfgang Stahl; Ha Vinh Lam Nguyen

The molecular-beam Fourier transform microwave spectrum of 2-acetyl-5-methylfuran is recorded in the frequency range 2-26.5 GHz. Quantum chemical calculations calculate two conformers with trans or cis configuration of the acetyl group, both of which are assigned in the experimental spectrum. All rotational transitions split into quintets due to the internal rotations of two nonequivalent methyl groups. By using the program XIAM, the experimental spectra can be simulated with standard deviations within the measurement accuracy, and yield well-determined rotational and internal rotation parameters, inter alia the V3 potentials. Whereas the V3 barrier height of the ring-methyl rotor does not change for the two conformers, that of the acetyl-methyl rotor differs by about 100 cm-1 . The predicted values from quantum chemistry are only on the correct order of magnitude.


ChemPhysChem | 2015

Conformational Transformations of Sulfur-Containing Rings: 2-Methyltetrahydrothiophene Gas-Phase Structures

Vinh Van; Christina Dindic; Ha Vinh Lam Nguyen; Wolfgang Stahl

Stable conformations of five-member rings with the prototype cyclopentane are well-known to exist as twist or envelope structures and are of general interest in chemistry. Here, we report on the conformational analysis of the sulfur-containing ring 2-methyltetrahydrothiophene studied by a combination of molecular beam Fourier transform microwave (MB-FTMW) spectroscopy and quantum chemistry. Two twist conformers were observed, whereby highly accurate molecular parameters could be determined. In addition, the (34) S-isotopologue of the most stable conformer was assigned in natural abundances. Geometry optimizations were performed at different levels of theory and the calculated rotational constants were compared with experimental values. Two transition states optimized at the MP2/6-311++G(d,p) level using the Berny algorithm could illustrate the intramolecular conversion between both conformers.


Journal of Physical Chemistry A | 2013

Sulfur-Containing Flavors: Gas Phase Structures of Dihydro-2-methyl-3-thiophenone

Halima Mouhib; Vinh Van; Wolfgang Stahl

Dihydro-2-methyl-3-thiophenone was investigated using a combination of quantum chemical calculations and molecular beam Fourier transform microwave spectroscopy. The substance is present in coffee, roasted peanuts, and whiskey. The microwave spectrum was recorded under molecular beam conditions in the frequency range from 9 to 14 GHz. We report on the two main conformers of dihydro-2-methyl-3-thiophenone, for which highly accurate rotational constants and centrifugal distortion constants were obtained. No splittings due to internal rotation of the methyl group could be observed in the microwave spectrum. This is in agreement with the theoretical predictions of the barrier heights, which have been determined to be more than 1000 cm(-1) at the MP2/6-311++G(d,p) level of theory. In addition to the most abundant (32)S-isotopologue of the main conformer, also the (34)S-isotopologue was assigned, which occurs with a natural abundance of about 4%. Using the experimental rotational constants, different quantum chemical calculations were validated for the two observed conformers. To complete the theoretical investigation of dihydro-2-methyl-3-thiophenone, different transition states were optimized to understand the intramolecular conversion between the two conformers at the MP2/6-311++G(d,p) level. The transition states were optimized using the Berny algorithm.


Astronomy and Astrophysics | 2016

Laboratory microwave, millimeter wave and far-infrared spectra of dimethyl sulfide

Atef Jabri; Vinh Van; Ha Vinh Lam Nguyen; Halima Mouhib; F. Kwabia Tchana; L. Manceron; Wolfgang Stahl; Isabelle Kleiner

Context. Dimethyl sulfide, CH 3 SCH 3 (DMS), is a nonrigid, sulfur-containing molecule whose astronomical detection is considered to be possible in the interstellar medium. Very accurate spectroscopic constants were obtained by a laboratory analysis of rotational microwave and millimeter wave spectra, as well as rotation-torsional far-infrared (FIR) spectra, which can be used to predict transition frequencies for a detection in interstellar sources. Aims. This work aims at the experimental study and theoretical analysis of the ground torsional state and ground torsional band ν 15 of DMS in a large spectral range for astrophysical use. Methods. The microwave spectrum was measured in the frequency range 2−40 GHz using two Molecular Beam Fourier Transform MicroWave (MB-FTMW) spectrometers in Aachen, Germany. The millimeter spectrum was recorded in the 50−110 GHz range. The FIR spectrum was measured for the first time at high resolution using the FT spectrometer and the newly built cryogenic cell at the French synchrotron SOLEIL. Results. DMS has two equivalent methyl internal rotors with a barrier height of about 730 cm -1 . We performed a fit, using the XIAM and BELGI-C s -2Tops codes, that contained the new measurements and previous transitions reported in the literature for the ground torsional state ν t = 0 (including the four torsional species AA, AE, EA and EE) and for the ground torsional band ν 15 = 1 ← 0 (including only the AA species). In the microwave region, we analyzed 584 transitions with J ≤ 30 of the ground torsional state ν t = 0 and 18 transitions with J ≤ 5 of the first excited torsional state ν t = 1. In the FIR range, 578 transitions belonging to the torsional band ν 15 = 1 ← 0 with J ≤ 27 were assigned. Totally, 1180 transitions were included in a global fit with 21 accurately determined parameters. These parameters can be used to produce a reliable line-list for an astrophysical detection of DMS.


Physical Chemistry Chemical Physics | 2015

Two equivalent methyl internal rotations in 2,5-dimethylthiophene investigated by microwave spectroscopy

Vinh Van; Wolfgang Stahl; Ha Vinh Lam Nguyen


Journal of Molecular Spectroscopy | 2018

The torsional barriers of two equivalent methyl internal rotations in 2,5-dimethylfuran investigated by microwave spectroscopy

Vinh Van; Jonas Bruckhuisen; Wolfgang Stahl; Vadim V. Ilyushin; Ha Vinh Lam Nguyen


Journal of Molecular Structure | 2016

The heavy atom microwave structure of 2-methyltetrahydrofuran

Vinh Van; Wolfgang Stahl; Ha Vinh Lam Nguyen

Collaboration


Dive into the Vinh Van's collaboration.

Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar

Vadim V. Ilyushin

National Institute of Standards and Technology

View shared research outputs
Top Co-Authors

Avatar

L. Manceron

Centre national de la recherche scientifique

View shared research outputs
Researchain Logo
Decentralizing Knowledge