The thermal desorption characteristics of 16 astrophysically relevant species from laboratory analogues of the icy mantles on interstellar dust grains have been surveyed in an extensive set of preliminary temperature programmed desorption experiments. The species can be separated into three categories based on behaviour. Water‐like species have a single relevant desorption coincident with water. CO‐like species show the volcano desorption and co‐desorption of trapped molecules, monolayer desorption from the surface of water ice, and multilayer desorption if initially present in sufficient abundance in an outer layer separated from the water ice. Intermediate species show the two desorptions of trapped molecules, and may show a small monolayer desorption for molecules small enough to have a limited ability to diffuse through the structure of porous amorphous water ice. Methods by which the results obtained under laboratory conditions can be adapted for astrophysical situations are discussed.

Hot cores and their precursors contain an integrated record of the physics of the collapse process in the chemistry of the ices deposited during that collapse. In this paper, we present results from a new model of the chemistry near high‐mass stars in which the desorption of each species in the ice mixture is described as indicated by new experimental results obtained under conditions similar to those in hot cores. Our models show that provided there is a monotonic increase in the temperature of the gas and dust surrounding the protostar, the changes in the chemical evolution of each species due to differential desorption are important. The species H2S, SO, SO2, OCS, H2CS, CS, NS, CH3OH, HCOOCH3, CH2CO, C2H5OH show a strong time dependence that may be a useful signature of time evolution in the warm‐up phase as the star moves on to the main sequence. This preliminary study demonstrates the consequences of incorporating reliable temperature programmed desorption data into chemical models.

Water (H2O) ice is an important solid constituent of many astrophysical environments. To comprehend the role of such ices in the chemistry and evolution of dense molecular clouds and comets, it is necessary to understand the freeze-out, potential surface reactivity, and desorption mechanisms of such molecular systems. Consequently, there is a real need from within the astronomical modelling community for accurate empirical molecular data pertaining to these processes. Here we give the first results of a laboratory programme to provide such data. Measurements of the thermal desorption of H2O ice, under interstellar conditions, are presented. For ice deposited under condi- tions that realistically mimic those in a dense molecular cloud, the thermal desorption of thin films (50 molecular layers) is found to occur with zero order kinetics charac- terised by a surface binding energy, Edes, of 5773 ±60 K, and a pre-exponential factor, A, of 1030±2 molecules cm−2 s−1. These results imply that, in the dense interstellar medium, thermal desorption of H2O ice will occur at significantly higher temperatures than has previously been assumed

The adsorption and desorption of CO on and from amorphous H 2 O ice at astrophysically relevant temperatures has been studied using temperature programmed desorption (TPD) and reflection-absorption infrared spectroscopy (RAIRS). Solid CO is able to diffuse into the porous structure of H 2 O at temperatures as low as 15 K. When heated, a phase transition between two forms of amorphous H 2 O ice occurs over the 30-70 K temperature range, causing the partial collapse of pores and the entrapment of CO. Trapped CO is released during crystallization and desorption of the H 2 O film. This behavior may have a significant impact on both gas-phase and solid-phase chemistry in a variety of interstellar environments.

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A novel plasma-assisted desorption/ionization (PADI) method that can be coupled with atmospheric pressure sampling mass spectrometry to yield mass spectral information under ambient conditions of pressure and humidity from a range of surfaces without the requirement for sample preparation or additives is reported. PADI is carried out by generating a nonthermal plasma which interacts directly with the surface of the analyte. Desorption and ionization then occur at the surface, and ions are sampled by the mass spectrometer. The PADI technique is demonstrated and compared with desorption electrospray ionization (DESI) for the detection of active ingredients in a range of over-the-counter and prescription pharmaceutical formulations, including nonsterodial anti-inflammatory drugs (mefenamic acid, Ibugel, and ibuprofen), analgesics (paracetamol, Anadin Extra), and Beecham's "all in one" cold and flu remedy. PADI has also been successfully applied to the analysis of nicotine in tobacco and thiosulfates in garlic. PADI experiments have been performed using a prototype source interfaced with a Waters Platform LCZ single-quadrupole mass spectrometer with limited modifications and a Hiden Analytical HPR-60 molecular beam mass spectrometer (MBMS). The ability of PADI to rapidly detect active ingredients in pharmaceuticals without the need for prior sample preparation, solvents, or exposed high voltages demonstrates the potential of the technique for high-throughput screening in a pharmaceutical or forensic environment.

Vapor-deposited amorphous water ice when warmed above the glass transition temperature (120-140 K), is a viscous liquid which exhibits a viscosity vs temperature relationship different from that of liquid water at room temperature. New studies of thin water ice films now demonstrate that viscous liquid water persists in the temperature range 140-210 K. where it coexists with cubic crystalline ice. The liquid character of amorphous water above the glass transition is demonstrated by (1) changes in the morphology of water ice films on a nonwetting surface observed in transmission electron microscopy (TEM) at around 175 K during slow warming, (2) changes in the binding energy of water molecules measured in temperature programmed desorption (TPD) studies, and (3) changes in the shape of the 3.07 micrometers absorption band observed in grazing angle reflection-absorption infrared spectroscopy (RAIRS) during annealing at high temperature. whereby the decreased roughness of the water surface is thought to cause changes in the selection rules for the excitation of O-H stretch vibrations. Because it is present over such a wide range of temperatures, we propose that this form of liquid water is a common material in nature. where it is expected to exist in the subsurface layers of comets and on the surfaces of some planets and satellites.

Abstract. The heterogeneous interaction of the stratospheric reservoir species HC1, C1ONO2, and N20 s with water-rich polar stratospheric particle mimics is characterized by the formation of solvated ionic products. Simple semiempirical calculations have been used to explain the nature of the species observed in infrared spectroscopic measurements and to elucidate the mechanism by which they are formed. The initial stages of the interaction appear to involve an SN2-type nucleophilic attack by the oxygen atom of the surface water molecule upon the most accessible electrophilic site of the adsorbing reactant. Mechanistic schemes involving protonated acid intermediates and their subsequent decomposition or hydrolysis can be used to accurately predict and explain the stable reaction products observed spectroscopically under stratospheric conditions.