High-resolution THz gain measurements in optically pumped ammonia

This study is aimed at the evaluation of THz gain properties in an optically pumped NH3 gas. NH3 molecules undergo rotational-vibrational excitation by mid-infrared (MIR) optical pumping provided by a MIR quantum cascade laser (QCL) which enables precise tuning to the NH3 infrared transition around 10.3 mu m. Pure inversion transitions, (J = 3, K = 3) at 1.073 THz and (J = 4, K = 4) at 1.083 THz were selected. The THz measurements were performed using a THz frequency multiplier chain. The results show line profiles with and without optical pumping at different NH3 pressures, and with different MIR tuning. The highest gain at room temperature under the best conditions obtained during single pass on the (3,3) line was 10.1 dBxm(-1) at 26 mu bar with a pumping power of 40 mW. The (4,4) line showed lower gain of 6.4 dBxm(-1) at 34 mu bar with a pumping power of 62 mW. To our knowledge these THz gains are the highest measured in a continuous-wave MIR pumped gas.Web of Science2616212482124

Millimeter-wave spectrum of 2-propanimine

Up to date, only 6 imines have been detected in the interstellar medium. The 3-carbon imine, 2-propanimine ((CH$_3$)$_2$C=NH), is predicted to be the structural isomer with the lowest energy in the C$_3$H$_7$N group, and appears to be a good candidate for astronomical searches. Unexpectedly, no microwave or millimeter wave spectrum is available for 2-propanimine. In this work, we provide the first high resolution millimeter wave spectrum of 2-propanimine and its analysis. With the guide of this laboratory measurement, we aim to search for 2-propanimine in two molecule-rich sources Sgr B2(N) and IRAS 16293-2422 using observations from the Atacama Large Millimeter/submillimeter Array (ALMA). Starting from a synthesized sample, we measured the spectrum of 2-propanimine from 50 to 500 GHz, and the ground state lines are successfully assigned and fitted using XIAM and ERHAM programs with the aid of theoretical calculations. The barriers to internal rotation of the two CH$_3$ tops are determined to be 531.956(64) cm$^{-1}$ and 465.013(26) cm$^{-1}$. These data are able to provide reliable prediction of transition frequencies for astronomical search. Although a few line matches exist, no confirmed detection of 2-propanimine has been found in the hot molecular core Sgr B2(N1S) and the Class 0 protostar IRAS 16293B. Upper-limits of its column density have been derived, and indicate that 2-propanimine is at least 18 times less abundant than methanimine in Sgr B2(N1S), and is at most 50-83 % of methanimine in IRAS 16293B.Comment: 14 pages, 10 figure

Characterising molecules for fundamental physics: an accurate spectroscopic model of methyltrioxorhenium derived from new infrared and millimetre-wave measurements

Precise spectroscopic analysis of polyatomic molecules enables many striking advances in physical chemistry and fundamental physics. We use several new high-resolution spectroscopic devices to improve our understanding of the rotational and rovibrational structure of methyltrioxorhenium (MTO), the achiral parent of a family of large oxorhenium compounds that are ideal candidate species for a planned measurement of parity violation in chiral molecules. Using millimetre-wave and infrared spectroscopy in a pulsed supersonic jet, a cryogenic buffer gas cell, and room temperature absorption cells, we probe the ground state and the Re=O antisymmetric and symmetric stretching excited states of both CH3 187 ReO3 and CH3 185 ReO3 isotopologues in the gas phase with unprecedented precision. By extending the rotational spectra to the 150-300 GHz range, we characterize the ground state rotational and hyperfine structure up to J = 43 and K = 41, resulting in refinements to the rotational, quartic and hyperfine parameters, and the determination of sextic parameters and a centrifugal distortion correction to the quadrupolar hyperfine constant. We obtain rovibrational data for temperatures between 6 and 300 K in the 970-1015 cm-1 range, at resolutions down to 8 MHz and accuracies of 30 MHz. We use these data to determine more precise excited-state rotational, Coriolis and quartic parameters, as well as the ground-state centrifugal distortion parameter D K of the 187 Re isotopologue. We also account for hyperfine structure in the rovibrational transitions and hence determine the upper state rhenium atom quadrupole coupling constant eQq'

THE ROTATIONAL SPECTRUM OF 13^{13}CH3_3NH2_2 UP TO 1 THz

This work is supported by the Programme National de Physico-Chimie du Milieu Interstellaire (PCMI-CNRS) and by the contract ANR-08-BLAN-0054.Author Institution: Laboratoire PhLAM, CNRS UMR 8523, Universite de Lille 1, 59655 Villeneuve d'Ascq Cedex, France; Institute of Radio Astronomy of NASU, Chervonopraporna 4, 61002 Kharkov, UkraineMethylamine (CH$_3$NH$_2$) is a molecule of astrophysical importance detected in interstellar medium for the first time in 1974~{\bf 191} (1974) L135.}. Also it has been discovered in the atmosphere of Jupiter~{\bf 4} (1977) 203. }. It is suggested that methylamine can be a precursor of the simplest amino acid glycine. In this context we present a new study of rotational spectrum of the ground vibrational state of $^{13}$C isotopologue of methylamine in the frequency range up to 1 THz. The spectrum of $^{13}$CH$_3$NH$_2$ was recorded and analyzed for the first time. All the spectra were obtained using the Lille spectrometer based on the solid state sources. The analysis of the rotational spectrum of methylamine is complicated by two large-amplitude motions: CH$_3$ torsion and NH$_2$ wagging. The Hamiltonian used in the present study is based on the group-theoretical high-barrier tunneling formalism developed by Ohashi and Hougen~{\bf 121} (1987) 474.}. This model proved to be efficient in the previous studies of the parent species of methylamine~{\bf 229} (2005) 170.} since it allowed fitting within experimental accuracy all the rotational transitions of the ground vibrational state with $J \leq 30$. In view of extended frequency range of the present study the fitting program will be modified in order to take into account the rotational transitions with $J > 30$. For the parent isotopic species, measurements and analysis using the same approach are in progress. The latest results will be discussed

High resolution millimeter-wave spectroscopy of cyclopropylphosphine-borane.

International audienceThe microwave spectrum of cyclopropylphosphine-borane, C(3)H(5)PH(2)-BH(3), has been investigated in the frequency range 150-195 GHz. The spectral assignment was supported by high level ab initio calculations. Two stable conformations have been predicted: the most stable antiperiplanar form and synclinal form that is higher in energy by 7.3 kJ/mol. In the observed spectra, only the most stable antiperiplanar (ap) form has been assigned. The analysis of the rotational spectra in the lowest excited vibrational states of the ap conformer has enabled determination of the potential function for the C-P torsional mode in the vicinity of equilibrium position. The barrier to internal rotation of the BH(3) top has been determined to be 9.616(15) kJ/mol and agrees well with quantum chemical calculations

MILLIMETER-WAVE SPECTROSCOPY OF AMINOMALONONITRILE

Author Institution: Laboratoire PhLAM, UMR 8523 CNRS - Universite Lille 1, 59655 Villeneuve d'Ascq Cedex, France; Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS - ENSCR, 35708 Rennes Cedex 7, France.This work is supported by the French program "Physique et Chimie du Milieu Interstellaire (PCMI, INSU-CNRS)" and the Centre National d'Etudes Spatiales (CNES).In low-temperature conditions of the interstellar medium pure HCN and mixtures of HCN with H$_2$O and NH$_3$ subjected to high-energy sources can be converted into different HCN polymers, 2004, 170, 203}. In this context the HCN trimer -- aminomalononitrile (AMN, H$_2$NCH(CN)$_2$) is an interesting candidate for astrophysical detection. We measured the rotational spectrum of AMN using the Lille BWO-based fast scan spectrometer (120 -- 180 GHz) and the spectrometer based on solid state sources (225 -- 250 GHz). The spectroscopic work was supported by high level \textit{ab initio} calculations. The spectra observed were assigned only to the asymmetric conformer. The first analysis revealed the regular doublet splittings of rotational lines indicating the possibility of large-amplitude motion (LAM) of amino group. Further examination of the spectra revealed the existence of additional splittings most probably due to the second LAM of amino group. Since the equilibrium structure of AMN has no symmetry, in the group theoretical formalism these two LAMs can be described using G$_4$ permutation-inversion group. Despite the complexity of the LAMs all the assigned rotational transitions were fitted within experimental accuracy using Pickett's SPFIT program. As a result, a reliable dataset for astrophysical observations was provided

Terahertz spectroscopy of deuterated formaldehyde using a frequency multiplication chain

International audienc

Speed dependence of CH335Cl-O2 line-broadening parameters probed on rotational transitions: measurements and semi-classical calculations

International audienceRelaxation parameters for K-components (K≤6) of six J→J+1 rotational transitions (J=6, 10, 17, 22, 31 and 33) of CH335Cl perturbed by O2 are measured at room temperature with Voigt, speed-dependent Voigt and Galatry profiles in order to probe the speed-dependence effects. With respect to the previous study of CH335Cl–N2 system [Guinet et al., J Quant Spectrosc Radiat Transfer 2012;113:1113], higher active-gas pressures are reached, providing better signal-to-noise ratios, and the exact expression of the Beer–Lambert law is introduced in the fitting procedure, leading, among other advantages, to much more realistic low-pressure results. The broadening parameters of the considered lines are also computed by a semi-classical method for various relative velocities of colliders and the powers characterizing the dependence of the collisional cross-sections on relative speeds are deduced as functions of the rotational numbers J and K. Additional calculations performed with the Maxwell–Boltzmann distribution of velocities show no significant difference with the earlier results [Buldyreva et al., Phys Chem Chem Phys 2011;13:20326] obtained within the mean thermal velocity approximation. Weighted sums of the presently measured Voigt-profile O2-broadening parameters and of the previously published N2-broadening ones are calculated to yield experimental air-broadening coefficients for spectroscopic databases

Laboratory spectroscopy of methoxymethanol in the millimeter-wave range

Methoxymethanol, CHOCHOH is a very interesting candidate for detection in the interstellar medium since it can be formed in the recombination reaction between two radicals considered as intermediates in methanol formation: CHO (already detected in the ISM) and CHOH. It could also be formed by the addition of CHO to formaldehyde (another abundant compound in the ISM) followed by abstraction of a hydrogen radical. In this study, we present the first spectroscopic characterization of methoxymethanol in the millimeter-wave range augmented by high level quantum chemical calculations. The analysis revealed three stable conformations all exhibiting different large amplitude motions (LAMs). For the analysis of the most stable conformation (I) we applied a model that accounts for hindered internal rotation of the methyl top. The analysis of conformation III was performed taking the interaction between the overall rotation and OH torsional motion into account. Conformation II was only tentatively assigned, as it exhibits several LAMs that significantly complicate the theoretical description. Accurate spectroscopic parameters obtained in this study provide a reliable basis for the detection of methoxymethanol in the ISM.Molecules interstellaires : spectroscopie et synthèse en laboratoir

Millimeter- and submillimeter-wave spectrum of trans-formaldoxime (CH

Context. Among the six atoms of N-containing molecules with the formula of CH3NO, only formamide (H2NCHO), the most stable structural isomer, has been detected in the interstellar medium (ISM). The formaldoxime isomer may be formed, for example, by the reaction of formaldehyde (H2CO) or methanimine (H2CNH) and hydroxylamine (H2NOH), which are all detected in the ISM. The lack of high accuracy millimeter- and submillimeter-wave measurements hinders the astronomical search for formaldoxime. Aims. The aim of this work is to provide the direct laboratory measurement of the millimeter- and submillimeter-wave spectrum of trans-formaldoxime. Methods. Formaldoxime was synthesized and its rotational spectrum was recorded at room temperature in a glass flow cell using the millimeter- and submillimeter-wave spectrometer in Lille. The SPFIT program in the CALPGM suite was used to fit the spectrum. Results. Rotational lines of trans-formaldoxime from both the ground state and v12 = 1 vibrational excited states have been measured and assigned from 150 to 660 GHz. Spectroscopic constants were derived to the tenth order using both Watson’s A and S reduction Hamiltonian