Spectroscopic characterization and photochemistry of nitrogen-containing molecules relevant to Titan's atmosphere

<p>Titan's atmospheric chemistry has been the source of intrigue since the planetary body's discovery. Though there is a growing understanding of the atmospheric chemistry of small molecules on Titan, much less is known about larger molecule formation, and particularly about nitrile chemistry. This dissertation characterizes nitrile/isonitrile intermediates that are postulated to be important in Titan's atmosphere, adding to the necessary foundation for understanding Titan's atmospheric chemistry. The vibronic spectroscopy of <em>para</em>-diisocyanobenzene (<em>p</em>DIB, C≡N-Ph-N≡C) has been characterized as a first step towards photochemical studies that can test the transformation of the isonitrile group to other nitrogen-based functionalities.<em>p</em>DIB was found to have a excitation spectrum dominated by Herzberg-Teller vibronic coupling to a nearby second electronic excited state, and the S₀-S₁origin was found to be weak, due to the near cancellation of the transition dipole moment upon electronic excitation. The phenylcyanomethyl radical (PCM, Ph-ĊH-C≡N), a doubly resonance-stabilized radical (RSR), was also spectroscopically characterized for the first time. The ionization potential, excited state lifetime, and rotational band contour of PCM at the D₀-D₁electronic origin were obtained. The spectroscopy of (E)- and (Z)-phenylvinylnitrile ((E)- and (Z)-PVN, Ph-CH=CH-C≡N), structural isomers of the simplest polycyclic aromatic nitrogen heterocycle (PANH) quinoline, was also characterized. Both (E)- and (Z)-PVN were found to be planar in the ground and first excited electronic state. (E)-PVN was found to participate in extensive Duschinsky mixing, whereas Duschinsky mixing was not as prominent in (Z)-PVN. The spectral signatures for (E)- and (Z)-PVN, were additionally used to carry out ultraviolet hole-filling (UVHF) experiments to test for the formation of quinoline through photoisomerization. Lastly, the microwave spectroscopy of 4-pentenenitrile (CH₂=CHCH₂CH₂C≡N), 4-pentynenitrile (N≡C-CH₂- CH₂-C≡CH), and glutaronitrile (N≡C-CH₂-CH₂-CH₂-C≡N) was studied. Microwave transitions of each molecule were assigned to particular conformations, providing high resolution microwave data that can be used in future microwave searches for their presence in Titan and elsewhere in interstellar space.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Year

2015

Author dc:creator

• Mehta-Hurt, Deepali N

Contributors dc:contributor

• Timothy Zwier
• Adam Wasserman
• Lyudmila Slipchenko
• Paul Wenthold

• Atmospheric Sciences
• Chemistry
• Environmental Chemistry

Repository record dc:identifier

https://docs.lib.purdue.edu/open_access_dissertations/516

OAI identifier oai:identifier

oai:docs.lib.purdue.edu:open_access_dissertations-1441