High-Resolution Spectroscopy Near the Continuum Limit: The Microwave Spectrum of Trans-3-Bromo-1,1,1,2,2-Pentafluoropropane


The microwave spectrum of 3-bromo-1,1,1,2,2-pentafluoropropane has been observed using CP-FTMW spectroscopy. Potential energy scans have been performed and confirm the existence of two conformers—trans and gauche—for which further structural optimisations and electric field gradient calculations have been performed in order to get highly accurate nuclear quadrupole coupling constants for assignment purposes. The combination of multiple conformers and large nuclear quadrupole coupling constants produce a very dense spectrum at an estimated 1 transition/MHz, near the continuum limit. This spectral density makes it necessary to have very sophisticated computational approaches in order to get geometric and electronic structures that are very close to experimental observation. Analysis of the spectrum allowed for the assignment of the trans conformer, but the gauche proved to be prohibitive, although it is believed to be present in the current spectrum. Full analysis of the rotational spectroscopic parameters of two isotopologues -- the 79Br and 81Br -- have been observed and are reported. Geometric analysis of the experimentally observed conformer is also reported using Kraitchman coordinate and second moments arguments. Further analysis of the spectrum reveals the occurrence of dipole-forbidden, nuclear quadrupole allowed transitions with one forbidden transition possessing the first known x-type forbidden transition linkage pathway.



Research Center/Lab(s)

Center for High Performance Computing Research


The authors would like to acknowledge the National Science Foundation (NSF-CHE-1841346), NASA Missouri EPSCoR Grant, Missouri S&T start-up funds, and the Missouri S&T OURE programme for financial support of this research.

Keywords and Phrases

continuum limit; CP-FTMW; forbidden transitions

International Standard Serial Number (ISSN)

0026-8976; 1362-3028

Document Type

Article - Journal

Document Version


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© 2018 Taylor & Francis Ltd., All rights reserved.

Publication Date

01 Sep 2019