Communication: Rotational g-factor and spin-rotation constant of CH+

Abstract

The rotational g-factor and spin-rotation constants of the methylidynium ion CH + have been calculated for the first time with a large multiconfigurational self-consistent field wave function and at the coupled-cluster singles and doubles level augmented by a perturbative triples correction. The results for an equilibrium internuclear distance as well as for the v =0, J = 1 vibration-rotational state are presented.

Effective potential energy curves of the ground electronic state of CH+

“…The results, shown in Tables VI and VII, compare well with the newest experimental values by Amano. 12,50 Compared with the previously calculated v = 0, J = 1 matrix elements, 32 which were obtained by solving the nuclear Schrödinger equation without any non-adiabatic contributions and with the CASSCF Born-Oppenheimer potential energy from the same work, we do not observe significant changes in the spinrotation constants but the deviation of the calculated rotational g-factor from the experimental value is halved and amounts now only to 0.5%. Rotational matrix elements v = 0, J |P |v = 0, J = P 0 + P r J (J + 1) − P rr J 2 (J + 1) 2 of the dipole moment operator P = μ (in a.u.…”

“…32,38,39,45,46 For an investigation of the dependence of the calculated properties on the one-electron basis set of Gaussian functions at an equilibrium internuclear distance (R = 2.137 a.u.) a complete active space self-consistent field (CASSCF) wavefunction was employed with 4 electrons in 15 molecular orbitals (7 of σ -, 3 of π -, and 1 of δ-symmetry) leading to 1185 configurations.…”

“…Furthermore, the cation has been investigated in several ab initio studies (see, e.g., Refs. [20][21][22][23][24][25][26][27][28][29][30][31][32] and can thus be classified as one of the best characterized interstellar particles, both experimentally and theoretically.…”

Theoretical study of the nuclear spin-molecular rotation coupling for relativistic electrons and non-relativistic nuclei. II. Quantitative results in HX (X=H,F,Cl,Br,I) compounds

“…The determination of the SR tensor is important in rotational spectrum measurements, as a tool for the analysis of molecular structure, and recently there have been several advances in the theoretical determination of this spectral parameter. [1][2][3][4][5][6][7][8][9][10][11][12][13] The SR tensor is also relevant for NMR spectroscopy as it was first shown by Ramsey,14 and extensively analyzed by Flygare, [15][16][17] that, in the non-relativistic (NR) domain, this property is related to the NMR nuclear magnetic shielding (NMS) tensor. Explicitly, the formal expression of its electronic contribution is equivalent to that of the so-called paramagnetic contribution to the absolute NMS tensor when it is calculated taking the molecular center of mass as gauge origin of the magnetic potential of the spectrometer magnetic field.…”

Theoretical study of the nuclear spin-molecular rotation coupling for relativistic electrons and non-relativistic nuclei

“…The spin-rotation tensor is also an interesting spectral parameter by itself in the analysis of molecular structure and recent advances have been published in the theoretical determination of this spectral parameter. [9][10][11][12][13][14][15][16][17][18][19] The theoretical relation linking the nuclear magnetic shielding tensor and the spin-rotation tensor is based in Larmor's theorem, which demonstrates the formal equivalence, in non-relativistic (NR) dynamics, of the Hamiltonian for a particle in a uniform magnetic field and in a uniformly rotating system, which holds up to first order in the field intensity. 20 However, in the presence of a heavy nucleus, relativistic dynamics must be applied in the study of the electronic distribution.…”