PRECISE SEMI-EXPERIMENTAL EQUILIBRIUM STRUCTURES OF SULFUR-CONTAINING HETEROCYCLES: THIOPHENE (C4H4S) AND THIAZOLE (C3H3NS)

Esselman, Brian J.

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Description

Title

PRECISE SEMI-EXPERIMENTAL EQUILIBRIUM STRUCTURES OF SULFUR-CONTAINING HETEROCYCLES: THIOPHENE (C4H4S) AND THIAZOLE (C3H3NS)

Author(s)

Esselman, Brian J.

Contributor(s)

McMahon, Robert J.; Woods, R. Claude; Stanton, John F.; Kobayashi, Kaori ; Sowin, Laura S.; Kougias, Samuel M.; Patel, Aatmik R.; Ichikawa, Yotaro ; Zdanovskaia, Maria ; Orr, Vanessa L.

Issue Date

24-Jun-20

Keyword(s)

Structure determination

Abstract

As has recently been demonstrated with pyrimidine, using multiple isotopic substitution combined with coupled-cluster calculations treating the vibration-rotation interaction and the electron mass, it is possible to determine highly precise semi-experimental equilibrium structures ($\it{r}$$_{e}$$^{SE}$). The CCSD(T)/cc-pCV5Z equilibrium structure of pyrimidine agrees with the $\it{r}$$_{e}$$^{SE}$ structure within the 2$\sigma$ uncertainties for all parameters. With the intent of improving the structure determinations of thiophene (8 – 360 GHz) and thiazole (130 -360 GHz), spectra have been collected. For each molecule, the main isotopologue vibrational ground state spectrum has been fit to a sextic Hamiltonian with low error ($\sigma$ $<$ 35 kHz). All heavy atom isotopologues ($^{34}$S, $^{13}$C, $^{15}$N, $^{33}$S) were detectable at natural abundance and similarly fit to sextic Hamiltonians. To obtain many more isotopologues, several deuteration strategies were employed: 1) acid-catalyzed H/D exchange, 2) base-catalyzed H/D exchange, and 3) lithium-halogen exchange using brominated forms of these species with subsequent addition of \chem{D_2O}. These samples have resulted in a total of over two dozen isotopologues for each of the sulfur-containing heterocycles, including multiple substitutions of each atom. The resulting $\it{r}$$_{e}$$^{SE}$ structures will be discussed, including an exploration of the number of isotopologues to sufficiently determine all parameters, computational treatment of the rotational constants, and comparison to theoretical $\it{r}$$_{e}$ structures containing sulfur. With pyrimidine, these structure determinations set a new standard of accuracy and precision for semi-experimental equilibrium structures ($\it{r}$$_{e}$$^{SE}$).

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

Text

Language

English

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