Spectroscopic studies of the internal modes of aminoaromatics by fluorescence excitation and dispersed emission in supersonic jet
A systematic study for the NH[sub 2] inversional mode in aniline and para substituted anilines has been performed using the techniques of fluorescence excitation and dispersed emission in supersonic jet. The transitions of the nitrogen inversion mode in aniline and para substituted anilines have been assigned in both the fluorescence excitation and dispersed emission spectra, which are strongly supported by the evidence of a large deuterium shift, the presence of a strong hot band, and the intense second overtone transition of the amino inversion in the excitation spectra of all the aniline molecules. The potential surface of each aniline has been fit using the observed inversional levels in both the ground and excited states. The molecular structure of each aniline has been investigated based on the experimental results. The NH[sub 2] torsional transition is assigned in the excitation spectrum of each aniline molecule for the first time. The absence of a torsional hot band and no observable tunneling splitting in the NH[sub 2] torsional mode indicates that the NH[sub 2] torsion mode in the anilines must have a very high first quanta in the ground state. The mechanism of I[sup 2][sub 0] and T[sup 2][sub 0] splittings in the excitation spectrum of p-toluidine has been explained by using molecular symmetry. The splittings are caused by the torsion-torsion coupling between the NH[sub 2] and CH[sub 3] groups. The structure of p-amino-p[prime]-methyl-trans-stilbene (PPTS) has been studied by spectroscopic methods and X-ray diffraction. The nearly planar geometry of the proton donor in the PPTS crystal dimer provides important evidence that the structure of gas phase PPTS is planar in the ground state. The absence of the hot band and I[sup 2][sub 0] in the excitation spectrum of PPTS indicates that the potential surface of PPTS must be a single well in both states, which is consistent with the X-ray result.
- Research Organization:
- Montana State Univ., Bozeman, MT (United States)
- OSTI ID:
- 6959073
- Country of Publication:
- United States
- Language:
- English
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