Ph.D. DISSERTATION DEFENSE: Collette C. Sarver
Widicus Weaver Group
Interstellar Complex Organic Molecules: From the Interstellar Medium to Star-Forming Regions
This dissertation combines laboratory experiments, observational astronomy, and
computational theory to study interstellar complex organic molecules (iCOMs) that are
relevant in the interstellar medium (ISM) and star-forming regions. First, interstellar ice
analogs of pure CH3OH and mixtures of H2O and CH3OH were studied under ultra-high
vacuum and cryogenic conditions with the Sublimation of Laboratory Ices
Millimeter/Submillimeter Experiment (SubLIME-UW). The effect of ultraviolet irradiation
with either simultaneous or subsequent temperature programmed desorption was
examined to mimic conditions in dense clouds and disks. Simultaneous results suggest
that comparing between different experiments and to interstellar conditions with fluence
but not flux or time held constant may be unreliable for mixed ices for some chemical
species. Ice mixtures in subsequent trials showed an enhancement of simpler species
and a suppression of complex species. Secondly, interferometric observations of NGC
1333 IRAS 4B and 4B’ with NOEMA are presented. Spectral line analysis identified 44
molecules and derived physical parameters (rotational temperature, column density,
velocity shift with respect to local standard of rest, and full-width-at-half-maximum spectral
line width) for 11 molecules towards IRAS 4B (10 were iCOMs), while no iCOM emission
was detected towards 4B’. Physical parameter and integrated intensity maps show 4B is
a binary protostar system that drives a jet in a north-south orientation and an outflow in a
northwest-southeast orientation and shows the first complete evidence of a west-east
outflow from 4B’. Finally, amorphous solid water (ASW) clusters, analogous to water on
interstellar ice grains, were investigated with quantum chemical electronic structure
calculations. As water dominates the ice coated grains within the ISM, studying subtle
nuances of water clusters can provide detailed information on the environment in which
iCOMs form. The goal of this work was to test the assumption that the addition of an
electron to an ASW cluster with a hydronium ion present would result in a neutralization
reaction. In all clusters studied, a neutralization reaction did not occur and the negative
charge became delocalized within the cluster.