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Description
Laboratory characterization (18-1893 GHz) and astronomical detection (IRAM-30m: 80-280GHz, Orion-KL) of CH_2_CHCN (vinyl cyanide) in its ground and vibrationally excited states. Improving the understanding of rotational spectra of vibrationally excited vinyl cyanide with new laboratory data and analysis. The laboratory results allow searching for these excited state transitions in the Orion-KL line survey. Furthermore, rotational lines of CH_2_CHCN contribute to the understanding of the physical and chemical properties of the cloud. Laboratory measurements of CH_2_CHCN made on several different frequency-modulated spectrometers were combined into a single broadband 50-1900GHz spectrum and its assignment was confirmed by Stark modulation spectra recorded in the 18-40GHz region and by ab-initio anharmonic force field calculations. For analyzing the emission lines of vinyl cyanide detected in Orion-KL we used the excitation and radiative transfer code (MADEX) at LTE conditions. Detailed characterisation of laboratory spectra of CH_2CHCN in 9 different excited vibrational states (v_11_=1, v_15_=1, v_11_=2, v_10_=1<==>(v_11_=1,v_15_=1), v_11_=3/v_15_=2/v_14_=1, (v_11_=1,v_10_=1)<==>(v_11_=2, v_15_=1), v_9_$=1, (v_11_=1,v_15_=2)<==>(v_10_=1, v_15_=1)<==>(v_11_=1,v_14_=1), and v_11_=4) and detection of transitions in the v_11_=2 and v_11_=3 states for the first time in Orion-KL, and of those in the v_10_=1<==>(v_11_=1,v_15_=1) dyad of states for the first time in space. The rotational transitions of the ground state of this molecule emerge from four cloud components of hot core nature which trace the physical and chemical conditions of high mass star forming regions in the Orion-KL Nebula. The lowest energy vibrationally excited states of vinyl cyanide such as v_11_=1 (at 328.5K), v_15_=1 (at 478.6K), v_11_=2 (at 657.8K), the v_10_=1<==>(v_11_=1,v_15_=1) dyad (at 806.4/809.9K), and v_11_=3 (at 987.9K) are populated under warm and dense conditions, so they probe the hottest parts of the Orion-KL source. The vibrational temperatures derived for the v_11_=1, v_11_=2, and v_15_=1 states are 252+/-76K, 242+/-121K, and 227+/-68K, respectively; all of them close to the mean kinetic temperature of the hot core component (210K). The total column density of CH_2_CHCN in the ground state is (3.0+/-0.9)x10^15^cm^-2^. We report the detection of methyl isocyanide (CH_3_NC) for the first time in Orion-KL and a tentative detection of vinyl isocyanide (CH_2_CHNC) and give column density ratios between the cyanide and isocyanide isomers obtaining a N(CH_3_NC)/N(CH_3_CN) ratio of 0.002. Laboratory characterisation of many previously unassigned vibrationally excited states of vinyl cyanide at microwave to THz frequencies allowed us to detect these molecular species in Orion-KL. Column density and rotational and vibrational temperatures for CH_2_CHCN in their ground and excited states, as well as for the isotopologues, have been constrained by means of a sample of more than 1000 lines in this survey.
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