L.H. Coudert

Detection of 15NH2D in dense cores : a new tool for measuring the 14N/15N ratio in the cold ISM

Context. Ammonia is one of the most reliable tracers of cold dense cores. It is also a minor constituent of interstellar ices and, as such, one of the important nitrogen reservoirs in the protosolar nebula, together with the gas phase nitrogen, in the form of N2 and N. An important diagnostic of the various nitrogen sources and reservoirs of nitrogen in the Solar System is the 14 N/ 15 N isotopic ratio. While good data exist for the Solar System, corresponding measurements in the interstellar medium are scarce and of low quality. Aims. Following the successful detection of the singly, doubly, and triply deuterated isotopologues of ammonia, we searched for 15 NH2D in dense cores, as a new tool for investigating the 14 N/ 15 N ratio in dense molecular gas. Methods. With the IRAM-30 m telescope, we obtained deep integrations of the ortho 15 NH2 D( 1 1,1–10,1) line at 86.4 GHz, simultaneously with the corresponding ortho NH2D line at 85.9 GHz. Results. The ortho 15 NH2 D( 1 1,0–10,1) is detected in Barnard-1b, NGC1333-DCO + , and L1689N, while we obtained upper limits towards LDN1544 and NGC1333-IRAS4A, and a tentative detection towards L134N(S). The para line at 109 GHz remains undetected at the rms noise level achieved. The 14 N/ 15 N abundance ratio in 15 NH2D ranges between 350 and 850, similar to the protosolar value of ∼424, and likely higher than the terrestrial ratio of ∼270.

Linelists for NH3, NH2D, ND2H, and ND3 with quadrupole coupling hyperfine components

Linelists for the ammonia molecule and its three deuterated variants NH 2 D, ND 2 H, and ND 3 are built taking hyperfine quadrupole coupling effects into account. For each hyperfine component, the line frequency, the line intensity, and the lower level energy are calculated.

Magnetic hyperfine coupling of a methyl group undergoing internal rotation: a case study of methyl formate.

The hyperfine structure of methyl formate was recorded in the 2-20 GHz range. A molecular beam coupled to a Fourier transform microwave spectrometer having an instrumental resolution of 0.46 kHz and limited by a Doppler width of a few kHz was used. A-type lines were found split by the magnetic hyperfine coupling while no splittings were observed for E-type lines. Symmetry considerations were used to account for the internal rotation of the methyl top and to derive effective hyperfine coupling Hamiltonians. Neglecting the spin-rotation magnetic coupling, the vanishing splittings of the E-type lines could be understood and analyses of the hyperfine patterns of the A-type lines were performed. The results are consistent with a hyperfine structure dominated by the magnetic spin-spin coupling due to the three hydrogen atoms of the methyl group.

THE FIRST ASTROPHYSICAL DETECTION, TERAHERTZ SPECTRUM, AND DATABASE FOR THE MONODEUTERATED SPECIES OF METHYL FORMATE HCOOCH2D

Based on new measurements carried out in the laboratory from 0.77 to 1.2 THz and on a line-frequency analysis of these new data, along with previously published data, we build a line list for HCOOCH2D that leads to its first detection in the Orion KL nebula. The observed lines, both in space and in the laboratory, involve the cis D-in-plane and trans D-out-of-plane conformations of HCOOCH2D and the two tunneling states arising from the large-amplitude motion connecting the two trans configurations. The model used in the line position calculation accounts for both cis and trans conformations, as well as the large-amplitude motion.

Ab initio intermolecular potential of Ar-C2H2 refined using high-resolution spectroscopic data

The high-resolution infrared spectra of the ν1 + ν3 (2CH) band of the Ar-C2H2 complex has been recorded from 6544 to 6566 cm(-1). The previously reported K(a) = 1 ← 0, 2 ← 1, and 0 ← 1 subbands were observed and the K(a) = 1 ← 2, 2 ← 3, and 3 ← 2 subbands were assigned for the first time. The intermolecular potential energy surface of this complex has been calculated ab initio and optimized by fitting the new high-resolution data. Refined intermolecular potential energy surfaces have been obtained for the ground vibrational state and for the excited v1 = v3 = 1 stretching state. For the former state, the results of the analysis are satisfactory and the microwave transitions of the complex are reproduced with a root-mean-square deviation of 5 MHz. For the latter state, systematic discrepancies arise in the analysis.

Analysis of the torsional spectrum of monodeuterated methanol CH2DOH

An analysis of the torsional spectrum of monodeuterated methanol CH(2)DOH is presented. Twenty nine torsional subbands have been assigned in the 20-800 cm(-1) region. The newly assigned subbands and those already available in the literature were analyzed with a theoretical approach accounting for internal rotation of an asymmetrical CH(2)D methyl group. Seventy six subband centers were reproduced with an rms value of 0.09 cm(-1). Spectroscopic parameters corresponding to the generalized inertia tensor and to the hindering potential were determined as well as rotation-torsion distortion constants.

The potential energy surface of the Ar-CO complex obtained using high-resolution data.

A potential energy surface is retrieved for the Ar-CO complex by carrying out a global analysis of its high-resolution spectroscopic data. The data set consists of already published microwave and infrared data and of new microwave transitions which are presented in the paper. The theoretical approach used to reproduce the spectrum is based on a model Hamiltonian which accounts simultaneously for the two large amplitude van der Waals modes and for the overall rotation of the complex. Only the vCO = 0 state is considered. The root-mean-square deviation of the analysis is 18 MHz for the microwave data and 1.4 x 10(-3) cm(-1) for the infrared energy difference data. Fifteen parameters corresponding to the potential energy function are determined in addition to two kinetic energy parameters and two distortion-type parameters. The potential energy surface derived is in good agreement with the one obtained by Shin, Shin, and Tao [J. Chem. Phys. 104, 183 (1996)].

The submillimeter-wave spectrum of the doubly deuterated species of methyl formate HCOOCD2H

Context. Astronomical surveys of interstellar molecules, such as those that will be available with the very sensitive ALMA telescope, require preliminary laboratory investigations of the microwave and submillimeter-wave spectra of new molecular species to identify these in the interstellar media. Aims: We build a linelist that should allow us to detect HCOOCD2H, provided it is present in the interstellar media in a suitable concentration. Methods: The experimental spectra of HCOOCD2H have been recorded in the microwave and submillimeter-wave energy range. Line frequencies were analyzed using an internal axis method-like treatment taking into account the CD2H internal rotation. Results: 5933 lines of HCOOCD2H have been assigned and their frequencies were reproduced with a unitless standard deviation of 1.6. A linelist with calculated frequencies and intensities was built and spans the 50 - 660 GHz spectral region. The frequency accuracy is better than 0.1 MHz. Conclusions: The pure rotation spectrum of the CD2H-methyl formate isotopolog (HCOOCD2H) has been observed in laboratory for the first time. Tables 3, 6, and 10 are available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/543/A46

Spin-torsion effects in the hyperfine structure of methanol

The magnetic hyperfine structure of the non-rigid methanol molecule is investigated experimentally and theoretically. 12 hyperfine patterns are recorded using molecular beam microwave spectrometers. These patterns, along with previously recorded ones, are analyzed in an attempt to evidence the effects of the magnetic spin-torsion coupling due to the large amplitude internal rotation of the methyl group [J. E. M. Heuvel and A. Dymanus, J. Mol. Spectrosc. 47, 363 (1973)]. The theoretical approach setup to analyze the observed data accounts for this spin-torsion in addition to the familiar magnetic spin-rotation and spin-spin interactions. The theoretical approach relies on symmetry considerations to build a hyperfine coupling Hamiltonian and spin-rotation-torsion wavefunctions compatible with the Pauli exclusion principle. Although all experimental hyperfine patterns are not fully resolved, the line position analysis yields values for several parameters including one describing the spin-torsion coupling.

Analysis of the microwave, terahertz, and far infrared spectra of monodeuterated methanol CH2DOH up to J = 26, K = 11, and o1

The first theoretical approach aimed at accounting for the energy levels of a non-rigid molecule displaying asymmetric-top asymmetric-frame internal rotation is developed. It is applied to a line position analysis of the high-resolution spectrum of the non-rigid CH2DOH molecule and allows us to carry out a global analysis of a data set consisting of already available data and of microwave and far infrared transitions measured in this work. The analysis is restricted to the three lowest lying torsional levels (e0, e1, and o1), to K ⩽ 11, and to J ⩽ 26. For the 8211 fitted lines, the unitless standard deviation is 2.4 and 103 parameters are determined including kinetic energy, hindering potential, and distortion effects parameters.