Interstellar water ice is mainly amorphous, but the nature of its morphology still remains poorly known. The experimental study described in this work focuses on how relevant changes of the ice morphology result from atomic hydrogen exposure and subsequent recombination. We show that there is an exponential decrease in the porosity of the amorphous water ice sample following hydrogen-atom irradiation. These and other laboratory results lead us to suggest that water ice in space is almost certainly amorphous and non-porous (compact).

We explore experimentally the formation of water molecules from O2 and D atoms on bare grains composed of amorphous silicates analogous to those in diffuse interstellar clouds. We provide the fractions of D2O and D2O2 molecules formed on the silicate surface held at 10 K from the O2 + D pathway using RAIRS and TPD techniques. For comparison, we also study the formation of water molecules on surfaces covered with amorphous water ice representing the dense clouds.

The formation of CO2 in quiescent molecular cores has long been of interest to astrochemists as CO2 is one of the most abundant solid phase molecules present in the interstellar medium. Previous studies have concentrated, for the most part, on formation mechanisms involving high energy particle or UV bombardment of ices, to mimic the influence of cosmic rays on solid phase species in the outer, lower density regions of molecular clouds. However, condensed phase CO2 is also observed in the inner, denser regions of clouds, where less UV radiation penetrates. To date, very few studies have been made of CO2 formation in the absence of energetic particles.

Low-energy routes to the formation of CO2 are crucial to explain the high abundances of this molecule observed in quiescent regions. We discuss recent experimental results of a study of the low-energy reaction CO + OH. A simple model, developed to describe the kinetics of the system, suggests that the various reactions of the OH radical are key in characterising the production of CO2 and other species. Our results indicate that some CO2 forms concurrently with H2O in molecular clouds, in line with both previous observations and theory. The results of this research are published in Noble et al. (2011).

We present a combined theoretical and experimental study of the adsorption of two pairs of organic isomers, (i) acetic acid AA (CH3COOH) and methyl formate MF (HCOOCH3), and (ii) ethanol EtOH (CH3CH2OH) and dimethyl ether DME (CH3OCH3), onto crystalline water ice surfaces at low temperatures. Both approaches show that, for each pair, the most stable isomer from a thermodynamical point of view, i.e. AA and EtOH, is also the one which is the more tightly bound to the water ice surface compared to the less stable isomers (MF and DME). This finding, which can be explained by the ability of AA or EtOH to efficiently interact with the ice surface via hydrogen bondings, may have important consequences in an astrophysical context, since it could explain why the most stable isomer is not the most abundant observed in the interstellar gas phase.

Since 1984 a change in the epidemiological pattern of meningococcal disease in Italy has occurred with a predominance of Neisseria meningitidis of serogroup C (76%), serotype 2a and a high proportion of strains resistant to sulphonamides (71%). In order to understand better the epidemiology of the group C N. meningitidis strains responsible for the disease over the last years in Italy, we studied the genetic features of phenotypically closely related strains, by enzyme electrophoresis. The results showed that the genetic and the phenotypic characteristics of the 57 strains studied were similar, suggesting the spread of a single clone during recent years in our country.

This result is in agreement with the circulation of strains typical of epidemic situations, despite the decreasing incidence of meningoccal disease in Italy.