Rafael Escribano

Ice structures, patterns, and processes: A view across the icefields

European Science Foundation workshop Euroice 2008 held in Granada, Spain from 1–4 October 2008; Spanish national project, Hielocris, financed by the Consejo Superior de Investigaciones Cientificas; funding from FWF, Austria (No. P23027); MINCINN, Spain (No. FIS2010-16455, No. PR2010-0012, and No. FIS2010-22322-528C02-02); and SNSF, Switzerland (No. 200021121857)

Raman spectroscopic characterization of carbonaceous aerosols

We have used Raman spectroscopy to characterize a variety of carbon-containing particulate matter, including samples collected in ambient urban atmospheres. Based on the Raman spectra of known, commercial particles, we derive a simple empirical model that reflects their microchemistry and microphysics. This model gives information on the crystal size and morphology of the graphitic component, which correlates with the known characteristics of the commercial samples. We derive similar information about the graphitic component of the ambient particles, and suggest that this method might be used to characterize ambient particles systematically in the future.

The ISO/SWS Spectrum of IRC +10216: The Vibrational Bands of C2H2 and HCN*

We present the Infrared Space Observatory/Short-Wavelength Spectrometer full grating resolution spectrum of IRC +10216, which is dominated by strong absorption/emission bands of C2H2 and HCN. All C2H2 bands and the strong near-infrared stretching bands of HCN are observed in absorption, whereas the fundamental, hot, and combination bands of HCN involving the nu2 bending mode around 14 µm are observed in emission. Particularly strong is the HCN nu2=20-->nu2=11 vibrational transition at 14.3 µm. The most plausible mechanism for such emission is the radiative pumping of molecules from the ground to the nu2=20 state (7.1 µm) followed by radiative decay: nu2=20-->nu2=11. We present detailed models for HCN that verify the efficiency of the mentioned effect. The HCN abundance inferred from these models is &parl0;1.5-3&parr0;x10-5.

Absolute Raman intensities of CH4, CH3D, CH2D2, CHD3, and CD4

Abstract Measurements of the absolute vibrational Raman intensities and depolarization ratios for the fundamental and some overtone and combination bands of CH 4 , CH 3 D, CH 2 D 2 , CHD 3 , and CD 4 are reported. Experimental aspects of these measurements are discussed. The experimental data conform satisfactorily to all isotope intensity sum rules. The measured intensities and depolarization ratios, together with the vibrational potential function for CH 4 , make possible the calculation of the four independent parameters of the isotopic invariant quantities α S = | ∂α ∂S | . The results deduced from these agree with all 36 experimentally observed values. Values of electro-optical parameters for the CH bond are calculated and discussed.

Spectroscopic constants for the ν9 infrared band of HNO3

Abstract High-resolution infrared measurements have been made on the ν 9 band of HNO 3 from 414 to 500 cm −1 . Over 2300 transitions have been measured, assigned, and fit to obtain 15 rovibrational constants for the v 9 = 1 state that reproduce the observed spectrum with a RMS deviation of 0.0004 cm −1 . The band center for ν 9 is at 458.2287 ± 0.0005 cm −1 .

Absolute Raman intensities, force constants, and electro-optical parameters of CH2Cl2, CD2Cl2 and CHDCl2

The absolute Raman intensities and depolarization ratios of all the fundamental bands of CH2Cl2, CD2Cl2 and CHDCl2 have been measured in the gas phase. These experimental data have been included in a refinement of the vibrational potential function of the dichloromethanes. A detailed description is made of the use of the bond polarizability approach. Explicit expressions for the derivatives of the molecular polarizability with respect to the symmetry coordinates are given in terms of the zeroth- and first-order electro-optical parameters of the theory. Good agreement is found between experimental and calculated intensities. The refined electro-optical parameters compare quite well with those obtained from methane, chloroform and carbon tetrachloride. The derivatives of the molecular polarizability with respect to the normal coordinates are also given.

A study of the interaction of CO2 with water ice

Aims. We studied the interaction between CO2 (guest) and H2O (host) molecular ices. Methods. Ices of CO2 and H2O are prepared by four di erent deposition techniques: sequential deposition (amorphous water ice followed by addition of CO2), co-deposition (both gases added simultaneously), inverse sequential deposition (carbon dioxide ice fol- lowed by addition of water) and crystalline sequential deposition (crystalline water ice is prepared first and CO2 is added afterwards). Samples are deposited at 80 K and are studied by temperature programmed desorption and transmission infrared spectroscopy. Results. Two slightly di erent varieties of association of CO2 and H2O are revealed from the di erent spectroscopic properties of the asymmetric stretching band of 12 CO2 and 13 CO2. The two varieties are found to co-exist in some of the samples at 80 K, whereas only the so-called internal CO2 remains after heating at 105 K. At 80 K carbon dioxide is able to adhere to a crystalline water ice surface. Activation energies for the desorption of CO2 from amorphous (Ed = 20:7 2 kJ mol 1 ) and crystalline (Ed = 19:9 2 kJ mol 1 ) water ice are derived from measurements of the sticking of CO2 as a function of ice temperature. Conclusions. These findings may have implications for the study of icy bodies of the Solar System.

Crystallization of CO2 ice and the absence of amorphous CO2 ice in space

Carbon dioxide (CO2) is one of the most relevant and abundant species in astrophysical and atmospheric media. In particular, CO2 ice is present in several solar system bodies, as well as in interstellar and circumstellar ice mantles. The amount of CO2 in ice mantles and the presence of pure CO2 ice are significant indicators of the temperature history of dust in protostars. It is therefore important to know if CO2 is mixed with other molecules in the ice matrix or segregated and whether it is present in an amorphous or crystalline form. We apply a multidisciplinary approach involving IR spectroscopy in the laboratory, theoretical modeling of solid structures, and comparison with astronomical observations. We generate an unprecedented highly amorphous CO2 ice and study its crystallization both by thermal annealing and by slow accumulation of monolayers from the gas phase under an ultrahigh vacuum. Structural changes are followed by IR spectroscopy. We also devise theoretical models to reproduce different CO2 ice structures. We detect a preferential in-plane orientation of some vibrational modes of crystalline CO2. We identify the IR features of amorphous CO2 ice, and, in particular, we provide a theoretical explanation for a band at 2,328 cm−1 that dominates the spectrum of the amorphous phase and disappears when the crystallization is complete. Our results allow us to rule out the presence of pure and amorphous CO2 ice in space based on the observations available so far, supporting our current view of the evolution of CO2 ice.

Empirical anharmonic force field and equilibrium structure of hypochlorous acid, HOCl

Abstract The cubic and quartic force fields of HOCl are investigated on the basis of the most recent experimental data on vibration-rotation interaction constants and anharmonicity constants. Some discrepancies with respect to previously reported ab initio results are found and discussed. The geometrical parameters of this molecule are also evaluated from recent data on the equilibrium values of the moments of inertia.

Absorption spectroscopy of SiH2 near 640 nm

The A 1B1–X 1A1 absorption spectrum of SiH2 has been observed using intracavity laser absorption spectroscopy with an equivalent path length of up to 13.0 km and the A 1B1(0,  0,  0)–X 1A1(0,  0,  0) band near 640 nm recorded for the first time. The silylene radical was generated in a continuous discharge in a flowing mixture of silane in argon, giving a concentration of the order of 1010 SiH2/cm3. The spectrum spans the region between 15350 and 16100 cm−1. Rotational transitions have been assigned to levels up to J=16 and Ka=9, with ΔKa up to 5, ΔKc up to 4. Perturbations have been detected in the spectrum, due to Renner–Teller and spin-orbit interactions between both electronic states and the 3B1 state, predicted to be between them. However, the strength of the irregular perturbations affecting the rotational states of A 1B1(0,0,0) state is found to be much weaker than that affecting the other (0,  v2′, 0) levels previously studied. The analysis of the spectrum has allowed the determination of the rot...