Spectroscopic investigation of fluoroiodomethane, CH2FI: Fourier-transform microwave and millimeter-/submillimeter-wave spectroscopy and quantum-chemical calculations

Abstract

Guided by theoretical predictions, the rotational spectrum of fluoroiodomethane, CH(2)FI, has been recorded and assigned. Accurate values are reported for the ground-state rotational constants, all quartic, sextic, and two octic centrifugal-distortion constants. The hyperfine structure of the rotational spectrum was thoroughly investigated using a Fourier-transform microwave spectrometer and the Lamb-dip technique in the millimeter-/submillimeter-wave region, thus allowing the accurate determination of the complete iodine quadrupole-coupling tensor and of the diagonal elements of the iodine spin-rotation tensor. Relativistic effects turned out to be essential for the accurate theoretical prediction of the dipole moment and quadrupole-coupling constants and were accounted for by direct perturbation theory and a spin-free four-component treatment based on the Dirac-Coulomb Hamiltonian. The relativistic corrections to the dipole moment amount to up to 34% and to the iodine quadrupole-coupling tensor to about 15-16% of the total values.

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.…”

Analytic energy derivatives in relativistic quantum chemistry

“…As relativistic effects are significantly larger for iodine than for bromine, DPT2 calculations are less reliable for the computational investigation of iodine compounds. For this reason, the joint theoretical and experimental investigation of CH 2 FI was based on SFDC‐CC calculations . In Table , our computational results are summarized and compared with the values derived from the experimental measurements.…”