Showing papers by "Maria Elisabetta Palumbo published in 1997"

Solid carbonyl sulfide (ocs) in dense molecular clouds

Abstract: An absorption feature at 2040 cm~1 (4.90 km), previously observed only in W33A, has been detected toward two deeply embedded young stellar objects (YSOs), AFGL 989 and Mon R2 IRS 2. Upper limits are reported for several other YSOs and for one object located behind the Taurus Dark Cloud. We attribute this interstellar feature to solid carbonyl sul-de (OCS) embedded in icy grain mantles along the line of sight. As in the case of W33A, the best match of the newly observed features with laboratory spectra of astrophysically relevant mixtures is obtained for traces of OCS in a methanol-rich matrix. This, again, suggests the presence of independent grain mantle populations and, in particular, of a minor fraction of methanol-rich icy grain mantles in which OCS is embedded. From the strength of the absorp- tion feature we deduce OCS column densities and ratios toward the observed objects. Taking OCS/H 2 O into consideration sulfur chemistry and the origins of solid OCS, we conclude that a major fraction of the elemental sulfur is presently unaccounted for in dense molecular clouds. Subject headings: infrared: ISM: lines and bands E ISM: clouds E ISM: molecules E line: identi-cation E molecular processes

Is it possible to detect frozen O_2_ and N_2_ on interstellar grains

Abstract: We continue to study the effects of ion irradiation on frozen ices with a view to their astrophysical relevance. The technique used to evidence molecular alteration is "in situ" in- frared (IR) spectroscopy. Here, we present results obtained ir- radiating by 3-60 keV helium and argon ions, frozen CO, and mixtures CO:O2 and CO:N2. The relevance of these studies for astrophysical applications is related to the fact that IR bands of frozen O2 and N2 are difficult to be observed. We investigate if their presence on ice mantles of interstellar grains could be evidenced through the changes in the CO profile or the presence of new species formed by energetic processing. The results in- dicate that the CO band at around 2140 cm 1 is only slightly modified by the simple mixing with the two non-polar species and, more deeply, by ion irradiation of the mixtures. Carbon dioxide (CO2) is the major species produced by irradiation. In CO:O2 mixtures ozone (O3) is produced at a large rate. Also car- bon suboxides are formed by ion irradiation of CO and CO:N2 mixtures, the profile of their bands is different in the two cases and can be used as tracer of the presence of N2 in icy mantles.