Ro-vibrational averaging of the isotropic hyperfine coupling constant for the methyl radical

Abstract

We present the first variational calculation of the isotropic hyperfine coupling constant of the carbon-13 atom in the CH3 radical for temperatures T = 0, 96, and 300 K. It is based on a newly calculated high level ab initio potential energy surface and hyperfine coupling constant surface of CH3 in the ground electronic state. The ro-vibrational energy levels, expectation values for the coupling constant, and its temperature dependence were calculated variationally by using the methods implemented in the computer program TROVE. Vibrational energies and vibrational and temperature effects for coupling constant are found to be in very good agreement with the available experimental data. We found, in agreement with previous studies, that the vibrational effects constitute about 44% of the constant's equilibrium value, originating mainly from the large amplitude out-of-plane bending motion and that the temperature effects play a minor role.

Variationally Computed IR Line List for the Methyl Radical CH3

“…The remaining PES-2 parameter values are identical to those of PES-1 and can be obtained from the supplementary material to Ref. 18.…”

“…18 c Computed using the P max = 32 basis set in conjunction with PES-2. 18 15 theoretical transition moments is given as Supporting Information and can be also found at www.exomol.com.…”

“…[11][12][13][14][15][16][17] In addition, CH 3 is an example of a molecule with large vibrational contribution to the hyperfine coupling constant, accounting for up to about 41% of the total value (see Ref. 18 and references therein).…”

The ExoMol project: Software for computing large molecular line lists

“…Apart from computing energies and spectra for a series of polyatomic molecules, the program TROVE has being applied to study some of their properties, for example, the so‐called rotational energy clustering or the temperature‐averaged nuclear spin–spin matrix elements and isotropic hyperfine coupling constant …”

“…A TROVE module for computing thermal averaging of a general molecular function based on Equations was implemented and applied to indirect nuclear spin–spin coupling constants and equilibrium structure of of ammonia and isotropic hyperfine coupling constant of methyl radical . The calculations require the ro‐vibrational eigenvalues E i and eigenvectors obtained by a time‐consuming matrix diagonalization.…”