J. Demaison

Rotational Spectrum and Tentative Detection of DCOOCH3-Methyl Formate in Orion

New centimeter-wave (7-80 GHz) and submillimeter-wave (580-661 GHz) spectra of a deuterated species of methyl formate (DCOOCH3) have been measured. Transitions with a maximum value of J = 64 and K = 36 have been assigned and fitted together with previous measurements. The internal rotation of this compound was treated using the so-called rho axis method. A total of 1703 transitions were fitted using this method. Only 24 parameters were employed in the final fit, which has an rms deviation of 94.2 kHz. The dipole moment and the nuclear quadrupole coupling constants of the deuterated specie have also been obtained. This new study has permitted a tentative detection of DCOOCH3 in Orion with the IRAM 30 m telescope based on the observation of more than 100 spectral features with low blending effects among the 400 lines expected in the observed frequency domain (for which over 300 are heavily blended with other species). These 100 transitions are above noise and confusion limited without heavy blending and cannot be assigned to any other species. Moreover, none of the strongest unblended transitions is missing. The derived source-averaged total column density for DCOOCH3 is 7.8 × 1014 cm–2 and the DCOOCH3/HCOOCH3 column density ratio varies between 0.02 and 0.06 in the different cloud components of Orion. This value is consistent with the deuteration enhancement found for other species in this cloud.

Rotational spectrum of deuterated and 15N ethyl cyanides: CH3CHDCN and CH2DCH2CN and of CH3CH2C15N

Context. Ethyl cyanide is an abundant molecule in hot molecular clouds. Its rotational spectrum is very dense and several hundreds of rotational transitions within the ground state have been identified in molecular clouds in the 40−900 GHz frequency range. Lines from 13 C isotopically substituted ethyl cyanide were identified in Orion. Aims. To enable the search and the possible detection of other isotopologues of ethyl cyanide in interstellar objects, we have studied the rotational spectrum of deuterated ethyl cyanide: CH2DCH2CN (in-plane and out-of-plane) and CH3CHDCN and the spectrum of 15 N substituted ethyl cyanide CH3CH2C 15 N. Using these experimental data, we have searched for these species in Orion. Methods. The rotational spectrum of each species in the ground state was measured in the microwave and millimeter-submillimeter wavelength range using a waveguide Fourier Transform spectrometer (8−17 GHz) and a source-modulated spectrometer employing backward-wave oscillators (BWOs) (150−260 and 580−660 GHz). More than 300 lines were identified for each species, for J values in the range 71−80 and Ka values in the range 28−31 depending on the isotopologues. The experimental spectra were analyzed using a Watson’s Hamiltonian in the A-reduction. Results. From the fitting procedure, accurate spectroscopic constants were derived for each of the species. These new sets of spectroscopic constants enable us to predict reliably the rotational spectrum (lines frequencies and intensities) in the 4−1000 GHz frequency range and for J and Ka up to 80 and 31, respectively. Combined with IRAM 30 m antenna observations of Orion, this experimental study allowed us to detect 15 N substituted ethyl cyanide CH3CH2C 15 N for the first time in Orion. The derived column density and rotational temperature are 10 13 cm −2 and 150 K for the plateau and 3 × 10 14 cm −2 and 300 K for the hot core. The deuterated species were searched for but were not detected. The upper limit to the column density of each deuterated isotopologues was 10 14 cm −2 .Context. Ethyl cyanide is an abundant molecule in hot molecular clouds. Its rotational spectrum is very dense and several hundreds of rotational transitions within the ground state have been identified in molecular clouds in the 40-900xa0GHz frequency range. Lines from 13 Cxa0isotopically substituted ethyl cyanide were identified in Orion. Aims. To enable the search and the possible detection of other isotopologues of ethyl cyanide in interstellar objects, we have studied the rotational spectrum of deuterated ethyl cyanide: CH 2 DCH 2 CN (in-plane and out-of-plane) and CH 3 CHDCN and the spectrum of 15 N substituted ethyl cyanide CH 3 CH 2 C 15 N. Using these experimental data, we have searched for these species in Orion. Methods. The rotational spectrum of each species in the ground state was measured in the microwave and millimeter-submillimeter wavelength range using a waveguide Fourier Transform spectrometer (8-17xa0GHz) and a source-modulated spectrometer employing backward-wave oscillators (BWOs) (150-260 and 580-660xa0GHz). More than 300xa0lines were identified for each species, for J xa0values in the range 71-80 and K a xa0values in the range 28-31 depending on the isotopologues. The experimental spectra were analyzed using a Watsons Hamiltonian in the A-reduction. Results. From the fitting procedure, accurate spectroscopic constants were derived for each of the species. These new sets of spectroscopic constants enable us to predict reliably the rotational spectrum (lines frequencies and intensities) in the 4-1000xa0GHz frequency range and for J and K a up toxa080 andxa031, respectively. Combined with IRAM 30xa0m antenna observations of Orion, this experimental study allowed us to detect 15 N substituted ethyl cyanide CH 3 CH 2 C 15 N for the first time in Orion. The derived column density and rotational temperature are 10 13 xa0cm -2 and 150xa0K for the plateau and 3xa0

Global assignment and extension of millimeter- and submillimeter-wave spectral database of 13C1-methyl formate (H13COOCH3) in the ground and first excited states

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13C-Methyl Formate: Observations of a Sample of High-mass Star-forming Regions Including orion-KL and Spectroscopic Characterization

10 14 xa0cm -2 and 300xa0K for the hot core. The deuterated species were searched for but were not detected. The upper limit to the column density of each deuterated isotopologues was 10 14 xa0cm -2 .

Ground state rotational spectrum, K = 3 splittings, ab initio anharmonic force field and equilibrium structure of trifluoroamine

A compilation of the available spectroscopic millimeter- and submillimeter-wave data of the ground and first excited states of 13C1-methyl formate (H13COOCH3) has been carried out. The exhaustive analysis of the available transition lines of H13COOCH3 has led to the assignment of 7457 spectral lines by means of a global fit of 45 parameters, using the Rho-Axis Method and the BELGI-Cs code, with a resulting unitless standard deviation of 0.57. Over 1600 lines are included for the first time in the fit. In addition, the line strengths of spectral lines are also calculated using the most recent experimental measurement of the electric dipole moment. In conclusion, the present study represents a notable improvement with respect to previous H13COOCH3 spectral analyses. Therefore, the better accuracy of the present analysis may help the future identification of new H13COOCH3 lines in the interstellar and circumstellar media, and may contribute to decrease some of the spectral confusion due to these species in astronomical surveys.

Microwave spectra of dimethylsulfide-d6, (CD3)2S, ground and excited torsional states

This work was supported by the National Science Foundation under grant 1008800. We are grateful to the Ministerio de Economia y Competitividad of Spain for the financial support through grant No. FIS2011-28738-C02-02 and to the French Government through grant No. ANR-08-BLAN-0054 and the French PCMI (Programme National de Physique Chimie du Milieu Interstellaire). This paper makes use of the following ALMA data: ADS/JAO. ALMA#2011.0.00009.SV.ALMAis a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. C.F. thanks Dahbia Talbi, Eric Herbst, and Anthony Remijan for enlightening discussions. Finally, we thank the anonymous referee for helpful comments.

Fourier transform infrared and millimeter-wave study of the v2=1, 2 and the v2=v4=1 rovibrational states of 14NF3

The submillimetre-wave spectrum of 14NF3 has been measured and the ground state rotational spectrum has been reanalysed, including the K=3 splittings. The quadratic, cubic and semidiagonal quartic force field has been calculated at the CCSD(T) level of theory employing a basis set of at least polarized valence triple-zeta quality. This force field has been used to predict the spectroscopic constants, including the parameters specific to the doubly degenerate vibrational states. The calculated values are found to be in good agreement with the available experimental data. The equilibrium structure has been derived from the experimental ground state rotational constants and either the ab initio or the experimental rovibrational interaction parameters. These experimental and semiexperimental structures are in excellent agreement with the ab initio equilibrium geometry.

Rotational spectra of CF3CN in the centimetre, millimetre and submillimetre wave ranges Observation of direct l -type resonance transitions

Abstract The microwave spectra of the molecular isotope (CD 3 ) 2 S in the ground state and the first and second excited states of methyl top torsion (internal rotation) and of CSC deformation as well as the ground-state spectra of the 13 C and 34 S substituted forms have been measured. The rotational constants and centrifugal distortion and rotation-vibration interaction constants could be determined. The rotational lines in the excited torsional states (1 1 , 1 2 , 2 1 , 2 2 , 2 3 ) were found to be split into quartets due to the interaction between molecular rotation and methyl top internal rotation. The experimental multiplet splittings were fitted to those calculated from a rotation-internal rotation Hamiltonian in order to obtain values for the internal rotation barrier V 3 and the top-top interaction potential coefficients V 12 and V ′ 12 . V 12 was too highly correlated with V 3 for a separate determination. The values following from the least-squares adjustment are discussed.

Equilibrium C-F Bond Length and the Structure of Formyl Fluoride, Difluorocarbene, Monofluoromethylene, and Difluoromethane

The 21 (A 1 ; 647.13cm - 1 ), 2 2 (A 1 ; 1292.26cm - 1 ) and 2 1 4 1 (E; 1138.28cm - 1 ) excited states of 1 4 NF 3 have been studied by high-resolution FTIR spectroscopy with a resolution between 2.3 and 3.0 x 10 - 3 cm - 1 ,and by millimeter-wave (MMW) spectroscopy. For the 2 1 state, 3380 non-zero weighted (NZW) υ 2 infrared (IR) transitions (J m a x =K m a x = 70) and 59 MMW transitions (J m a x = 27, K m a x = 21) were fitted together, with respective rms deviations σ I R = 0.142 x 10 - 3 cm - 1 and σ M M W = 28 kHz, using an unperturbed model up to sextic centrifugal distortion constants. The lower state parameters were constrained to those of the ground state. Similarly we have fitted 2181 NZW transitions (J m a x = K m a x = 60) of the 2υ 2 - υ 2 hot band merged with 54 MMW transitions (J m a x = 21, K m a x = 13) measured in the 2 2 state and employing the 2 1 parameters for the lower state. Respective rms deviations were σ I R = 0.263 x 10 - 3 cm - 1 and σ M M W = 58 kHz. The anharmonicity constant x 2 2 = -1.00606(1)cm - 1 was determined. The υ 2 = 2 state is better determined by the 2υ 2 - υ 2 rather than the obtained 2υ 2 IR data owing to the weakness of 2v 2 . To the contrary the strong and isolated υ 2 + υ γ 1 4 combination band is much better suited to probe the 2 1 4 1 state than the υ 2 + υ γ 1 4 - υ γ 1 4 hot band. Therefore 4375 NZW IR lines (J m a x =K m a x = 69) of v 2 + v 4 and 119 MMW transitions belonging to the 2 1 4 1 state with J m a x = K m a x = 13 were fitted together using the same model as for the v 4 fundamental band. This model takes into account l(2, 2), l(2,-1), l(2, -4), and (0, 6) intravibrational interactions when the D reduction of the Hamiltonian is employed. The corresponding rms of deviations were σ I R = 0.270 x 10 - 3 cm - 1 and σ M M W = 227 kHz; similar rms values were also obtained for Q and QD reductions refining uniformly 22 parameters. The anharmonicity constant x 2 4 = -2.27995(3) cm - 1 was determined.

Submillimeter-Wave Spectrum and Structure of Acrylonitrile

Rotational spectra of the ground, ν = 1, ν7= 1 and ν8 = 1 vibrational states of trifluoroacetonitrile, CF3CN, have been measured in the millimetre and submillimetre wave range and analysed. The ground state spectrum has been extended up to 650 GHz (J = 109) and sextic centrifugal distortion constants have been determined accurately. The ν4 = 1 and ν7 = 1 spectra have been measured up to 350 GHz (J = 51), and improved molecular constants have been obtained. By means of microwave Fourier transform spectroscopy, the nuclear quadrupole hyperfine structures of the J = 1-0 transitions for the vibrational states ν8 = 1,2,3, have been measured and analysed. Using the same experimental technique 431 direct l-type resonance transitions (section rule ΔJ=0, Δk=Δl=±2) in the vibrational state ν8=1 have been observed up to J= 85 which were partly split by nuclear quadrupole coupling. The analysis of these splittings was based on the theory of Aliev, M. R., and Hougen, J. T., 1984, J. molec. Spectrosc., 106, 110. An acc...