ANNUAL REPORT 2011 - Instituto de Estructura de la Materia

spectroscopy and mass spectrometry. By means of a recently acquired cryostat we can extend our experimentalrange down to 6 K covering a temperature interval very interesting in astrophysics. In the following paragraphs wedescribe in more detail the main contributions achieved during the last year.We have initiated a line of research with some astrobiological propensity. The molecule of glycine has been detectedon cometary grains, and a comprehensive spectroscopic investigation of this species in different environments andphysical conditions was not yet available. We therefore performed a spectroscopic study of glycine in its neutral andionic structures, isolated and in polar and non-polar environments, and followed changes in its structure for a rangeof temperatures between 25 and 200 K. To sublimate solids with low vapour pressure, like the aminoacid glicine, wehave designed and built a mini-oven that allows volatilizing the sample under vacuum and depositing its vapor on acold substrate. We have also improved the experiment adding a system to rotate the substrate under vacuum. Wewill continue this line, applied to other biological species.Concerning astrophysically relevant molecules, carbonic acid has been claimed to exist in different environments, asfor example in Mars atmosphere or forming part of cometary comae. For the first time, we have observed thismolecule in gas phase in the laboratory. This experimental and theoretical study has been done in collaboration withDr. Grothe’s and Dr. Lortieng’s groups from Vienna and Innsbruck Universities respectively. This investigation hasreceived a notorious international repercussion being even announced in the web page of CSIC.Other problem treated in this astrophysical line has dealt with the detection of deuterated water and the D/H isotopicexchange in amorphous and crystalline ice below 150 K. The molecular isotopic distributions hold valuable clues forunderstanding the properties and evolution of astronomical environments. In our investigation, we conclude thatdetectable HDO/H2O ratios may range from a few percent for amorphous samples to a few per thousand incrystalline ice, using the OD stretching band as probe. These relative high lower limits of detection and theappreciable dependence of the band shape on temperature will complicate the interpretation of data from many linesof sight. We have also investigated the structure and spectroscopic properties of the formate ion, HCOO - , a speciesof astrophysical relevance. The formate ion is characterized by its plasticity, adopting several different structures.We have studied the ion in crystals of sodium formate and ammonium formate, and as an isolated species. Thetheoretical calculations were contrasted by comparison to observed infrared spectra recorded using differenttechniques.In the atmospheric line of research, we have carried out, in collaboration with colleagues of the ComplutenseUniversity and the University of Isparta (Turkey), a theoretical investigation on mixtures of hydrogen chloride, nitricacid and a number of water molecules, from 1 to 6. We have predicted their infrared spectra and studied especiallytheir proton transfer and hydrogen bond characteristics. We have devised a method to classify these clusters in termsof their hydrogen bond strength and degree of ionization. In collaboration with colleagues from Vienna and the UK,we have collected a set of results of the application of different spectroscopic techniques to nitric acid monohydrate,a molecule related to atmospherically relevant species.In addition to this line, we have performed a theoretical study on the molecular properties of intra-molecularhydrogen bonds, and halogen bondings in the iodo-tyrosine molecule. This investigation was carried out incollaboration with Drs. Gómez and Pacios, from UCM and UPM respectively.We also continue with the set-up of a new flow chamber dedicated to the production and study of atmosphericaerosols. The chamber is nearly ready and the first results are expected during 2012.The main results of this line are reflected in the corresponding publications as indicated later on in this Memory.Kinetics of cold plasmas and studies on plasma-surfaces interactionsThe effect of comparatively small pressure changes ( 0.5 - 3 Pa), on the characteristics of low pressure hollowcathode dc discharges of H 2 , Ar/H 2 mixtures and air has been investigated with a combination of experimentaltechniques and kinetic models. In all cases, sudden characteristic changes were observed, which have been mostuseful in the identification of key physicochemical processes in these plasmas.Isotope exchange in low pressure cold plasmas of H 2 /D 2 mixtures has been studied by mass spectrometry of neutralsand ions, and kinetic modeling. These plasmas are of interest in fusion devices and in interstellar chemistry, as wellas in technological processes involving the deposition of hydrogen containing films. The measurements, whichinclude also electron temperatures and densities, have been performed in a stainless steel hollow cathode dischargereactor at different pressures and relative compositions. The data have been analyzed with a model developed by us,showing good global agreement. The dissociation of the fuel gas molecules is followed by wall recycling, whichregenerates H 2 and D 2 , and produces HD. Atomic recombination at the wall is found to proceed through an Eley–67