Observational Results of a Multi-Telescope Campaign in Search of Interstellar Urea [(NH2_2)2_2CO]

In this paper, we present the results of an observational search for gas phase urea [(NH$_2$)$_2$CO] observed towards the Sgr B2(N-LMH) region. We show data covering urea transitions from $\sim$100 GHz to 250 GHz from five different observational facilities: BIMA, CARMA, the NRAO 12 m telescope, the IRAM 30 m telescope, and SEST. The results show that the features ascribed to urea can be reproduced across the entire observed bandwidth and all facilities by best fit column density, temperature, and source size parameters which vary by less than a factor of 2 between observations merely by adjusting for telescope-specific parameters. Interferometric observations show that the emission arising from these transitions is cospatial and compact, consistent with the derived source sizes and emission from a single species. Despite this evidence, the spectral complexity, both of (NH$_2$)$_2$CO and of Sgr B2(N), makes the definitive identification of this molecule challenging. We present observational spectra, laboratory data, and models, and discuss our results in the context of a possible molecular detection of urea.Comment: 38 pages, 9 Figures, accepted in the Astrophysical Journa

WHAT IS THE NATURE OF THE DOUBLETS IN THE E-METHANOL LAMB-DIP SPECTRA?

Author Institution: Institute of Applied Physics of RAS, 46 Ul'yanova str., GSP-120, Nizhny Novgorod 603950; RussiaA large number of methanol lines have been measured with a Lamb-dip technique in the frequency range 75-510 GHz. A few series of doublets for the transitions with selection rules $\Delta J$ = 0, $\Delta K$ = $\pm$ 1, $\pm$ 3, $\pm$ 5, $E_1 \leftrightarrow E_2$ and $\Delta J$ = $\pm$ 1, $\Delta K$ = $\pm$ 1 between the torsional-rotational levels of E-methanol in the $\nu_t$ = 0 state have been observed. These doublets were not predicted and were not observed earlier. In a traditional approach to the methanol molecule (as a nearly prolate asymmetric top with an internal rotation) these doublets may only originate from the magnetic hyperfine structure of the $E$-methanol torsional-rotational levels. However, there are some signs in spectra indicating that the doublets are sensitive to the parity selections rules. If so, the origin of the doublets is an inversion splitting of the $E(+)$ and $E(-)$ energy levels. This exciting interpretation seems to be feasible. The results of the experimental measurements will be presented and the possibility of a new type of the inversion motion in the CH$_3$OH molecule due to the proton tunneling in the H-O-C-H plane will be discussed

COMPARATIVE STUDIES of J′←J=1←0J'\leftarrow J = 1 \leftarrow 0 CO LINE BROADENING PARAMETERS IN FREQUENCY AND TIME DOMAIN EXPERIMENT

$^{g}$H.Maeder, A.Guarnieri, J. Doose N.Nissen, V.N.Markov, A.M stanyuk A.F.Andianov A.F.Krupnov, Jocn Mole Spectr. 180, 183-187(1996) $^{h}$Support by DFG and RFBR grams is gratefully acknowledgedAuthor Institution: Institut f\""ar Physikalische Chemie, University Kiel; Institut f\""ar Physikalische Chemie, Institute of Applied Physics of Russian Academy of ScienceThe pressure broadening of CO $J^{\prime}\leftarrow J = 1 \leftarrow 0$ line has been studied by Two different techniques. The investigation was made with the perturber gases $CO^{g}, N_{2}, O_{2}, H_{2}, CO_{2}, He, Ne, Ar, Kr,$Xe at room temperature. The two different methods of line broadening measurement and the results obtained in the time- and in the frequency-domain respectively will be discused. Both methods gave results in a good agreement, for example, selfbroadening parameter $C_{w} = 3.43(2)$ MHZ/TORR(time-domain) and $C_{w} = 3.425(6)$ (frequency-domain) were $obtained.^{h}

CO-Ar collisions: ab initio model matches experimental spectra at a sub percent level over a wide pressure range

International audienceWe use three independent spectroscopic techniques, operating in the millimeter-wavelength range, to study molecule-atom collisions, and validate our quantum-scattering calculations on two recent potential energy surfaces. We study the first pure rotational transition in a CO molecule perturbed by Ar. This molecular system is a good prototype of atmospherically relevant cases. It is, on the one hand, affordable for calculation of the line shape parameters by modern ab initio methods, and on the other hand, is very convenient for experimental studies because of its regular, well spaced rotational spectrum having a moderate intensity. We show that the simulated collision-perturbed spectra, which are based on our fully ab initio calculations, agree with the experimental line profiles at sub-percent level over a wide range (more than four orders of magnitude) of pressures. We demonstrate that the agreement between theory and experiment can be further improved if the model accounts for the collisional transfer of an optical coherence between different rotational transitions (the line-mixing effect). We show that the two surfaces tested in this work lead to a very similar agreement with the experiment. Capability of calculating line shape parameters in a broad range of temperatures is demonstrated