Spectroscopie rotationnelle

Résumé

La spectroscopie rotationnelle, de rotation ou micro-onde étudie l'absorption et l'émission d'une onde électromagnétique (habituellement dans la région micro-onde du spectre électromagnétique) par des molécules associées aux modifications correspondantes du nombre quantique de rotation de la molécule. L'utilisation de micro-ondes en spectroscopie a été rendue possible en raison principalement du développement de la technologie associée pour le radar durant la Seconde Guerre mondiale. La spectroscopie rotationnelle n'est réellement possible qu'en phase gazeuse quand le mouvement de rotation est quantifié. Le spectre de rotation d'une molécule (au premier ordre) nécessite que la molécule possède un moment dipolaire et que les centres de charge et masse soient distincts, ou, de manière équivalente, qu'il existe une différenciation de deux charges distinctes. C'est l'existence de ce moment dipolaire qui permet au champ électrique de la lumière (micro-onde) d'exercer un couple sur la mol

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LABORATORY DETECTION OF HOCN AND TENTATIVE IDENTIFICATION IN Sgr B2

Sandra Bruenken

The rotational spectrum of cyanic acid, HOCN, has been detected in the centimeter-wave band in a molecular beam by Fourier transform microwave spectroscopy and in the millimeter-wave band by conventional spectroscopy in a low-pressure laboratory discharge. Spectroscopic constants, including the nitrogen hyperfine coupling constant, derived from 31 a-type transitions between 21 and 360 GHz with J up to 17 and K-a

2009

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Detection Of Vibrationally Excited Co In Irc+10216

Sandra Bruenken

Using the Submillimeter Array we have detected the J = 3-2 and 2-1 rotational transitions from within the first vibrationally excited state of CO toward the extreme carbon star IRC+10216 (CW Leo). The emission remains spatially unresolved with an angular resolution of similar to 2 '' and, given that the lines originate from energy levels that are similar to 3100 K above the ground state, almost certainly originates from a much smaller (similar to 10(14) cm) sized region close to the stellar photosphere. Thermal excitation of the lines requires a gas density of similar to 10(9) cm(-3), about an order of magnitude higher than the expected gas density based on previous infrared observations and models of the inner dust shell of IRC+10216.

2009

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Polycyclic Aromatic Hydrocarbons (PAHs) are widely accepted as the carriers of the Aromatic Infrared Bands (AIBs), but an unambiguous identification of any specific interstellar PAH is still missing. For polar PAHs, pure rotational transitions can be used as spectral fingerprints for identification. Combining dedicated experiments, detailed simulations and observations, we explore d the mm wavelength domain to search for specific rotational transitions of corannulene (C20H10). We performed high-resolution spectroscopic measurements and a simulation of the emission spectrum of ultraviolet-excited C20H10 in the environment of the Red Rectangle (RR), calculating its synthetic rotational spectrum. Based on these results, we conducted a first observational campaign at the IRAM 30-m telescope towards this source to search for several high-J rotational transitions of C20H10. The laboratory detection of the J = 112 134 transition at 137.615 GHz. Comparing the noise level with the synthetic spectrum, we are able to estimate an upper limit to the fraction of carbon locked in corannulene of about 1.0 x 10(-5) relative to the total abundance of carbon in PAHs. The sensitivity achieved in this work shows that radio spectroscopy can be a powerful tool to search for polar PAHs. We compare this upper limit with models for the PAH size distribution, emphasizing that small PAHs are much less abundant than predicted. We show that this cannot be explained by destruction but is more likely related to the chemistry of their formation in the environment of the RR.

Blackwell Publishing Ltd, Oxford2009

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