Experimental investigations of molecules desorbing from a cold surface with buffer gas cooling and broadband roational spectroscopy : applications in astrochemistry

This thesis presents the description of a novel instrument which couples buffer gas cooling with chirped-pulse Fourier transform mm-wave rotational spectroscopy and its successful applications in the study of molecules desorbing from an ice under interstellar-like conditions. The instrument, chirped-pulse ice (CPICE) offers conformer specific detection of molecules in the 60-90 GHz region using broadband mm- wave rotational spectroscopy, giving it significant relevance in the context of molecular radioastronomy which continues to enrich our understanding of the molecular complexity in the interstellar medium. Furthermore, CPICE is geared to investigate the formation and quantification of complex organic molecules upon the slow warmup of energetically processed interstellar ice analogs with precision. CPICE is discussed, showing how the design and its many components amalgamate to achieve the task of coupling buffer gas cooling with mm- wave broadband rotational spectroscopy. Normal propyl cyanide (n-PrCN) is used to obtain broadband rotational spectra and to determine the effective rotational temperature of molecules within the buffer gas cell following direct vapor injection into the cell. The 1.7GHz broadband spectra shows unambiguous detection of n-PrCN conformers and a rotational temperature of 30K, ~5K higher than the buffer gas cell temperature (25K) is determined. The detection of H2CO following temperature programmed desorption of VUV processed CH3OH ices deposited on a 4K substrate verifies CPICE's ability to investigate the formation of complex organic molecules using interstellar ice analogs. The conformer distributions of gauche-n-PrCN and anti-n-PrCN is also investigated in the gas phase following room-temperature gas injection and from molecules desorbing from an ice deposited at 4K. the room temperature conformer distribution is used to derive the relative energy difference between the two species where the gauche conformer was found to be more stable by 97[plus or minus]21 cm-1. Following further examination of the relative conformer abundances from ice desorption, distinct from the direct gas injection, ratios correspond to a conformer temperature of ~ 56 K, which is much lower than their sublimation temperature of 170 K.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Masters

Discipline thesis:degree_discipline

Chemistry (MU)

Grantor dc:publisher

University of Missouri--Columbia

Year dc:date.issued

2024

Author dc:creator

• Kanaherarachchi, Anudha Chitresha

Advisor dc:contributor.advisor

• Broderick, Bernadette M.

Language dc:language.iso

eng, English

DOI

https://doi.org/10.32469/10355/107827

OAI identifier oai:identifier

oai:mospace.umsystem.edu:10355/107827