Internal Rotation Of The Acetyl Methyl Group In Methyl Alkyl Ketones: The Microwave Spectrum Of Octan-2-one

Methyl \textit{n}-alkyl ketones form a class of molecules with interesting internal dynamics in the gas-phase. They contain two methyl groups undergoing internal rotations. To explore the link between structure and barrier heights in ketones, investigations on a series of saturated methyl \textit{n}-alkyl ketones were performed, i.e. pentan-2-one\footnote{M. Andresen, I. Kleiner, M. Schwell, W. Stahl, H. V. L. Nguyen, J. Phys. Chem. A 2018, 122, 7071-7078} hexan-2-one\footnote{M. Andresen, I. Kleiner, M. Schwell, W. Stahl, H. V. L. Nguyen, ChemPhysChem 2019, 20, 2063-2073}, heptan-2-one\footnote{M. Andresen, I. Kleiner, M. Schwell, W. Stahl, H. V. L. Nguyen, J. Phys. Chem. A 2020, 124, 1353-1361.} and octan-2-one\footnote{M. Andresen, D. Schöngen, I. Kleiner, M. Schwell, W. Stahl, H. V. L. Nguyen, ChemPhysChem 2020, 21, 2206-2216}. The molecular jet Fourier-transform microwave spectrum of octan-2-one was recorded between 2.0 and 40.0 GHz, revealing two conformers, one with C$_{1}$ and one with C$_{s}$ symmetry. The barriers to internal rotation of the acetyl methyl group were determined to be 233.340(28) cm$^{-1}$ and 185.3490(81) cm$^{-1}$, respectively, confirming the link between conformation and barrier height already established for other methyl alkyl ketones. The study combined high level \textit{ab initio} calculations with experimentally dervived rotational and torsional parameters using the XIAM\footnote{H. Hartwig, H. Dreizler, Z. Naturforsch. 1996, 51a, 923-932} and BELGI-C$_{1}$ (or BELGI-C$_{s}$)\footnote{I. Kleiner, J. T. Hougen, J. Chem. Phys. 2003, 119, 5505-5509.} codes. Results from the various fits will be presented. Finally comparisons to molecules in the literature and structural aspects of the conformers generally observed in methyl \textit{n}-alkyl ketones will be reviewed

Laboratory rotational spectrum and astronomical search of s-methyl thioformate

Methyl thioformate CH$_{3}$SC(O)H, is a monosulfur derivative of methyl formate, a relatively abundant component of the interstellar medium (ISM)\footnote{E. Chruchwell, G. Winnewisser, A\&A, 45, 229 (1975)}. Methyl thioformate being the thermodynamically most stable isomer with a C$_{2}$H$_{4}$OS formula, it can be reasonably proposed for detection in the ISM. Theoretical investigations on this molecule have been done recently by Senent et al.\footnote{M. L. Senent, C. Puzzarini, M. Hochlaf, R. Domínguez-Gómez and M. Carvajal, J. Chem. Phys., 141, 104303 (2014)}. Previous experimental studies on this molecule have been performed by Jones et al.\footnote{G. I. L. Jones, D. G. Lister and N. L. Owen, J. Mol. Spectrosc., 60, 348 (1976)} and Caminati et al.\footnote{W. Caminati, B. P. V. Eijck and D. G. Lister, J. Mol. Spectrosc., 90, 15 (1981)} and its microwave spectrum was recorded between 10 and 41 GHz.\\ In this study, S-methyl thioformate has been synthesized by reaction of methyl mercaptan with formic-acetic anhydride. The millimeter wave spectrum was then recorded for the first time from 150 to 660 GHz with the Lille’s spectrometer based on solid-state sources \footnote{O. Zakharenko, R. A. Motiyenko, L. Margul\`es, T. R. Huet., J. Mol. Spectrosc., 317, 41 (2015)}. Around 2300 lines were assigned up to $J = 70$ and $K = 15$ and a fit for the ground torsional state $\nu_{t}=0$ performed with the \textit{BELGI-C$_{s}$} code\footnote{J. T. Hougen, I. Kleiner, and M. Godefroid, J. Mol. Spectrosc. 163, 559 (1994)} will be presented and discussed. Our aim is to provide a line list for an astrophysical research

A SIMULTANEOUS FIT OF vt = 0 AND 1 TORSION-WAGGING-ROTATIONAL LEVELS OF METHYLAMINE USING A HYBRID (TUNNELING AND NON-TUNNELING) HAMILTONIAN FORMALISM

This work is in memory of Dr. Jon Hougen deceased on January 28th 2019 who dedicated his life to spectroscopy and worked on the present project very actively untill the end of December 2018. We will show the latest results obtained with Jon on the fit of more than 15000 rotational-torsional-wagging transitions in the MW and FIR of v$_{t}$ = 0,1 of \chem{CH_3NH_2}. We used the recently written hybrid program to fit rotational levels in molecules with one \chem{CH_3} internal-rotation large-amplitude motion, one \chem{NH_2} inversion large-amplitude motion, and symmetry described by the G$_{12}$ PI group\footnote{J. T. Hougen and I. Kleiner, J. Phys. Chem. A, 2015, 119, 10664}. We will first present an overview of our present best least-squares fit. The data set contains slightly less than 2500 MW and 12754 FIR transitions, which are fit to a weighted standard deviation of 1.13 using 74 parameters. Most of the FIR transitions are taken from recent measurements of the v$_{t}$ = 1-0 band centered near 265 \wn \footnote{I. Gulaczyk, M. Kreglewski, V.-M. Horneman, J. Mol. Spectrosc. 2017,342, 25}, but a number of lines were re-assigned or remeasured. The ground torsional state (taken mostly from Motyienko et al\footnote{R.A. Motiyenko, V.V. Ilyushin, B.J. Drouin, S. Yu, L. Margulès, Astron.and Astrophys. 2014, 563, A1}) fit within measurement uncertainty but 75 older MW measurements in the v$_{t}$ = 1 showed large observed-calculated residuals and were presently discarded from the fit. We believe that our fit, as well as the predictive abilities of the program, are now sufficiently good that we can begin a new measurement campaigns of v$_{t}$ = 1 MW data and v$_{t}$ = 2, 3 IR data. This new project will be discussed in the talk\footnote{Part of this work has been funded by the Programme National de Physique Chimie du Milieu Interstellaire (PCMI)}

Экологические проблемы информационной цивилизации

Цель данного исследования - проясниться характерные черты академического взгляда, подготовленные революцией в информационной сфере. Задача, установленная автором, рассмотреть возможные проблемы, которые создает информационная цивилизация. Методологической основой для достижения поставленных целей и решения проблем является систематический подход.The purpose of this study is to clarify the features of the scientific worldview prepared by the information revolution. The task posed by the author lies in the field of considering possible problems created by the information civilization. The methodological basis for achieving the goals and solutions of the assigned task is the system-activity approach

MICROWAVE SPECTROSCOPY OF 2-PENTANONE

Methyl propyl ketone (MPK) or 2-Pentanone is known to be an alarm pheroromone released by the mandibular glands of the bees._x000d_ It is a highly volatile compound. This molecule was studied by a combination of quantum chemical calculations and microwave _x000d_ spectroscopy in order to get informations about the lowest energy conformers and their structures.The rotational spectrum of 2-pentanone was measured using the molecular beam Fourier transform microwave spectrometer in Aachen operating between 2 and 26.5 GHz. Ab initio calculations determine 4 conformers but only two of them are observed in our jet-beam conditions.The lowest conformer has a $C_{1}$ structure and its spectrum shows internal rotation splittings arising from two methyl groups. The internal splittings of 305 transitions for this conformer were analyzed using the XIAM code footnote{ H. Hartwig, H. Dreizler, Z. Naturforsch. 51a, 923 _x000d_ (1996).}. It led to the determination of the values for the barrier heights hindering the internal rotation of two methyl groups_x000d_ of 239 cm$^{-1}$ and 980 cm$^{-1}$ respectively. The next energy conformer has a $C_{s}$ structure and the analysis of the internal splittings of 134 transitions using the XIAM code and the BELGI code footnote{J. T. Hougen, I. Kleiner and M. Godefroid, J. Mol. Spectrosc., 163, 559-586 (1994).} led to the determination of internal rotation barrier height of 186 cm$^{-1}$. Comparisons of quantum chemistry and experimental results will be discussed

COMPETITION BETWEEN TWO LARGE-AMPLITUDE MOTION MODELS: NEW HYBRID HAMILTONIAN VERSUS OLD PURE-TUNNELING HAMILTONIAN

In this talk we report on our progress in trying to make the hybrid Hamiltonian competitive with the pure-tunneling_x000d_ Hamiltonian for treating large-amplitude motions in methylamine. A treatment using the pure-tunneling model has _x000d_ the advantages of: (i) requiring relatively little computer time, (ii) working with relatively uncorrelated fitting_x000d_ parameters, and (iii) yielding in the vast majority of cases fits to experimental measurement accuracy. These _x000d_ advantages are all illustrated in the work published this past year on a gigantic $v_{t}$ = 1 data set for the torsional_x000d_ fundamental band in methyl aminefootnote{I. Gulaczyk, M. Kreglewski, V.-M. Horneman, J. Mol. Spectrosc., in Press_x000d_ (2017).}. A treatment using the hybrid model has the advantages of: (i) being able to carry out a global fit _x000d_ involving both $v_{t}$ = 0 and $v_{t}$ = 1 energy levels and (ii) working with fitting parameters that have a clearer _x000d_ physical interpretation. Unfortunately, a treatment using the hybrid model has the great disadvantage _x000d_ of requiring a highly correlated set of fitting parameters to achieve reasonable fitting accuracy, which _x000d_ complicates the search for a good set of molecular fitting parameters and a fit to experimental accuracy. _x000d_ At the time of writing this abstract, we have been able to carry out a fit with J up to 15 that includes all _x000d_ available infrared data in the $v_{t}$ = 1-0 torsional fundamental band, all ground-state microwave data with _x000d_ K up to 10 and J up to 15, and about a hundred microwave lines within the $v_{t}$ = 1 torsional state, _x000d_ achieving weighted root-mean-square (rms) deviations of about 1.4, 2.8, and 4.2 for these three categories of data._x000d_ We will give an update of this situation at the meeting._x000d

A NEW HYBRID PROGRAM FOR FITTING ROTATIONALLY RESOLVED SPECTRA OF METHYLAMINE-LIKE MOLECULES: APPLICATION TO 2-METHYLMALONALDEHYDE

A new hybrid-model fitting program for methylamine-like molecules has been developed, based on an effective Hamiltonian in which the ammonia-like inversion motion is treated using a tunneling formalism, while the internal-rotation motion is treated using an explicit kinetic energy operator and potential energy function. The Hamiltonian in the computer program is set up as a 2x2 partitioned matrix, where each diagonal block consists of a traditional torsion-rotation Hamiltonian (as in the earlier program BELGI), and the two off-diagonal blocks contain all tunneling terms. This hybrid formulation permits the use of the permutation-inversion group $G_{6}$ (isomorphic to $C_{3v}$) for terms in the two diagonal blocks, but requires $G_{12}$ for terms in the off-diagonal blocks. Our first application of the new program is to 2-methylmalonaldehyde. Microwave data for this molecule were previously fit (essentially to experimental measurement error) using an all-tunneling Hamiltonian formalism to treat both large-amplitude-motions footnote{V.V. Ilyushin, E.A. Alekseev, Yung-Ching Chou, Yen-Chu Hsu, J. T. Hougen, F.J. Lovas, L. Picraux, J. Mol. Spectrosc. 251 (2008) 56-63}. For 2-methylmalonaldehyde, the hybrid program achieves a fit of nearly the same quality as that obtained by the all-tunneling program, but fits with the hybrid program eliminate a large discrepancy between internal rotation barriers in the OH and OD isotopologues of 2-methylmalonaldehyde that arose in fits with the all-tunneling program. Other molecules for application of the hybrid program will be mentioned

COUPLED LARGE AMPLITUDE MOTIONS: THE EFFECTS OF TWO METHYL INTERNAL ROTATIONS AND 14N QUADRUPOLE COUPLING IN 4,5-DIMETHYLTHIAZOLE

The molecular jet Fourier-transform microwave spectrum of 4,5-dimethylthiazole has been recorded between 2.0 and 26.5 GHz, revealing torsional splittings arising from two inequivalent methyl internal rotations with relatively low hindering barriers and nitrogen quadrupole hyperfine structures. Two global fits of 97 rotational transitions with 315 torsional and 1009 hyperfine components involving 5 torsional species were performed using the program \textit{XIAM} \footnote{H. Hartwig, H. Dreizler, Z. Naturforsch. 51a, 923–932, 1996.} and \textit{BELGI-C$_{s}$-2Tops-hyperfine}, an extended version of the \textit{BELGI-C$_{s}$-2Tops} code \footnote{M. Tudorie, I. Kleiner, J.T. Hougen, S. Melandri, L.W. Sutikdja, W. Stahl,J. Mol. Spectrosc.269, 211-225, 2011.} which includes the effect of the $^{14}$N quadrupole coupling, giving a root-mean-square deviation of 399.8 kHz and 4.2 kHz, respectively. Compared to the monomethyl substituted thiazole derivatives, the barriers to internal rotation are drastically lower. This is also in contrast to chemical intuition which suggests high barriers due to steric hindrance. Because of the strong interaction between the methyl groups, strong top-top couplings in both the potential energy and kinetic parts of the Hamiltonian were observed

Prospects for high-resolution microwave spectroscopy of methanol in a Stark-deflected molecular beam

Recently, the extremely sensitive torsion-rotation transitions in methanol have been used to set a tight constraint on a possible variation of the proton-to-electron mass ratio over cosmological time scales. In order to improve this constraint, laboratory data of increased accuracy will be required. Here, we explore the possibility for performing high-resolution spectroscopy on methanol in a Stark-deflected molecular beam. We have calculated the Stark shift of the lower rotational levels in the ground torsion-vibrational state of CH3OH and CD3OH molecules, and have used this to simulate trajectories through a typical molecular beam resonance setup. Furthermore, we have determined the efficiency of non-resonant multi-photon ionization of methanol molecules using a femtosecond laser pulse. The described setup is in principle suited to measure microwave transitions in CH3OH at an accuracy below 10^{-8}

Highly correlated ab initio study of the far infrared spectra of methyl acetate

Highly correlated ab initio calculations (CCSD(T)) are used to compute gas phase spectroscopic parameters of three isotopologues of the methyl acetate (CH3COOCH3, CD3COOCH3, and CH3COOCD3), searching to help experimental assignments and astrophysical detections. The molecule shows two conformers cis and trans separated by a barrier of 4457 cm−1. The potential energy surface presents 18 minima that intertransform through three internal rotation motions. To analyze the far infrared spectrum at low temperatures, a three-dimensional Hamiltonian is solved variationally. The two methyl torsion barriers are calculated to be 99.2 cm−1 (C–CH3) and 413.1 cm−1 (O–CH3), for the cis-conformer. The three fundamental torsional band centers of CH3COOCH3 are predicted to lie at 63.7 cm−1 (C–CH3), 136.1 cm−1 (O–CH3), and 175.8 cm−1 (C–O torsion) providing torsional state separations. For the 27 vibrational modes, anharmonic fundamentals and rovibrational parameters are provided. Computed parameters are compared with those fitted using experimental data