Synthesis, High-Resolution Millimeter-Wave Spectroscopy, and Ab Initio Calculations of Ethylmercury Hydride

Abstract

The millimeter-wave rotational spectrum of an organomercury compound, ethylmercury hydride, has been recorded and assigned for the first time. The spectroscopic study is complemented by quantum chemical calculations taking into account relativistic effects on the mercury atom. The very good agreement between theoretical and experimental molecular parameters validates the chosen ab initio method, in particular its capability to predict accurate quartic centrifugal distortion constants related to this type of compound. Estimations of the nuclear quadrupole coupling constants have less predictive power than those of the structural parameters, but are good enough to satisfy the spectroscopic needs. In addition, the orientation of the axis of the H-Hg-C bonds deduced from the experimental nuclear quadrupole coupling constants compares well with the corresponding ab initio value. From the good agreement between experimental and theoretical results, together with the observation of the six most abundant isotopes of mercury, ethylmercury hydride is unambiguously identified as the product of the chemical reaction described here, and its calculated equilibrium geometry is confirmed.

Perturbative treatment of spin-orbit coupling within spin-free exact two-component theory

“…These sets are in the following referred to as ANO1 and have been obtained by recontracting the ANO-RCC primitive sets for the SFX2C-1e scheme. 87 The corresponding rotational constants for this geometry, A = 29 656 MHz, B = 2816 MHz, and C = 2654 MHz, are moderately accurate in comparison to the experimental values of A = 29 303 MHz, B = 2755 MHz, and C = 2597 MHz, 68 with relative errors of around 1%-2%. Non-relativistic and SFX2C-1e HF, CCSD, and CCSD(T) calculations for the efg at the Hg nucleus were performed to enable a systematic analysis of both scalar-relativistic and electron-correlation effects.…”

“…The rotational spectrum of ethylmercury hydride (HHgCH 2 CH 3 ) has recently been recorded and analyzed by Goubet et al 68 Density functional theory calculations of the 201 Hg quadrupole-coupling constants using the spinfree Douglas-Kroll-Hess (SFDKH) scheme in order to account for scalar-relativistic effects have been used to facilitate the analysis of the spectrum and have been shown to yield qualitatively correct results. It should be noted that adequate treatments of relativistic and electron-correlation effects are required for accurate calculations of 201 Hg quadrupolecoupling parameters.…”

“…24 We also report a chemical application of the scheme to the computation of the second-order SOC corrections to the 201 Hg quadrupole-coupling constants of the ethylmercury hydride (HHgCH 2 CH 3 ) molecule recently characterized using rotational spectroscopy. 68 In Sec. V we present a summary and an outlook on future development.…”

Towards the Detection of Explosive Taggants: Microwave and Millimetre‐Wave Gas‐Phase Spectroscopies of 3‐Nitrotoluene

“…The NQC tensor χ i , j , after conversion from RAM into PAM ( i , j = a , b , c ), has been diagonalised in the principal axes system of the 14 n nucleus ( i , j = x , y , z ) to link the NQC constants to the molecular geometry and to the electronic structure ( χ i , j = eQq ij with e the electric charge of the proton, Q the quadrupole moment, and q ij the molecular electric field gradient). This diagonalisation implies the calculation of the α angle between the principal axis α of the molecule and the principal axis z of the nucleus oriented, in a first approximation, along the internuclear axis C‐N . The α values, determined both from experimental and calculated NQC parameters, are in good agreement.…”

“…The NQC tensor c i,j ,a fter conversion from RAM into PAM( i,j = a,b,c), has been diagonalised in the principal axes system of the 14 n nucleus( i,j = x,y,z)t ol ink the NQC constantst ot he molecular geometry andt ot he electronic structure (c i,j = eQq ij with e the electric charge of the proton, Q the quadrupole moment, and q ij the molecular electric field gradient). Thisd iagonalisation implies the calculation of the a angle between the principal axis a of the molecule and the principal axis z of the nucleus oriented,i nafirst approximation, along the internuclear axis C-N. [39,40] The a values, determined both from experimental and calculated NQC parameters, are in good agreement. Finally,t he electric field gradient orientation can be evaluated with the asymmetry parameter h ¼ c xx Àc yy c zz .I nT able 4, the experimental and calculated values of h indicateastrong deviation of the electric field gradientf rom the usually admitted cylindrical symmetry around the z-axis almost coincident with the CÀN bond.I ndeed, the two experimental h values are very close to 0.45 and the calculated h values are always > 0.5.…”