The UV spectroscopy of 3-phenyl-2-propynenitrile and it's methylated derivatives

2019-06-11T16:16:06Z (GMT) by Khadija M Jawad

For decades there has been interest in understanding early prebiotic Earth, including its atmospheric chemistry. Saturn’s moon Titan is the only other body in our Solar System with an atmosphere thought to resemble that of early Earth’s, and for this reason it has garnered a lot of attention over the years. Much is now known about the smaller molecules present in that atmosphere, starting with the most abundant, N2 and CH4, and going up to slightly larger molecules such as cyanoacetylene and benzene. As the molecules get larger, however, so does the gap in knowledge, especially as it pertains to nitriles. This dissertation aims to add to the story of Titan’s nitriles by first characterizing a molecule thought to be the photochemical product of the reaction between cyanoacetylene and benzene, 3-phenyl-2-propyne-nitrile (PPN). The UV spectra of PPN proved immensely interesting due to the strong presence of in-plane and out-of-plane vibrations of b2 and b1 symmetry, respectively. This is possibly a result of strong vibronic coupling between several excited electronic states or Coriolis coupling between complementary b1 and b2 vibrational levels. The multi-layer extension of the multi-configuration time dependent Hartree (ML-MCTDH) algorithm was used to understand how the excited states and the vibrational levels might interact, and emission and absorption spectra were modeled and compared to the experimental spectra. The second group of molecules studied included the ortho-, meta-, and para-methyl PPN. Strong methyl rotor activity is seen in the m-methyl PPN, with some activity in the p-methyl PPN. The methyl rotor activity in the m-methyl PPN is similar to other meta-substituted toluenes, and allows us to describe the methyl rotor barrier height in both ground and excited electronic state. Additionally, in all three methylated PPNs we see evidence for strong vibronic coupling in the abundance of out-of-plane vibrations, as had been seen in PPN.