A reliable ab initio potential energy surface and vibrational states for the ground electronic state of HgH2(XΣg+1)

Abstract

A three-dimensional global potential energy surface for the ground (X (1)Sigma(+)(g))electronic state of HgH(2) is constructed from more than 13,00 ab initio points. These points are generated using an internally contracted multireference configuration interaction method with the Davidson correction and a large basis set. Low-lying vibrational energy levels of HgH(2), HHgD, and HgD(2) calculated using the Lanczos algorithm are found to be in good agreement with the available experimental band origins. The majority of the vibrational energy levels up to 9000 cm(-1) are assigned with normal mode quantum numbers. Our results indicate a gradual transition for the stretching vibrations from the normal mode regime at low energies to the local mode regime near 9000 and 8000 cm(-1) for HgH(2) and HgD(2), respectively, as evidenced by a decreasing energy gap between the (0,0,n(3)) and (1,0,n(3)-1) vibrational states and bifurcation of the corresponding wave functions.

Infrared Emission Spectra and Equilibrium Structures of Gaseous HgH2 and HgD2

“…The absolute vibrational energies of the 100 ( ) and 01 1 0 (Π u ) states, that is, ν 1 and ν 2 , could not be determined from our data. The best ab initio values for ν 1 of HgH 2 and HgD 2 are 1982 cm -1 and 1421 cm -1 , respectively . The neon matrix values for ν 2 of HgH 2 and HgD 2 are 782 cm -1 and 562 cm -1 , respectively …”

“…There have been several ab initio theoretical studies of the electronic structure and geometry of gaseous HgH 2 , predicting a linear H−Hg−H structure and a closed-shell X̃ 1 ground electronic state. − The equilibrium Hg−H internuclear distances estimated by various theoretical models were in the range of 1.615−1.713 Å. − For a heavy atom like Hg, relativistic effects are significant and should be included in the calculations. Nonrelativistic calculations overestimate the Hg−H internuclear distance by more than 0.1 Å. − Harmonic vibrational frequencies of HgH 2 , HgHD, and HgD 2 have been calculated at the DFT(B3LYP), MP2, and CCSD(T) levels of theory with relatively large basis sets. − Recently, Li et al performed a very high level ab initio calculation on this molecule and predicted the energies for many vibrational levels of HgH 2 , HgHD, and HgD 2 for J = 0 (no rotation) using a variational calculation. They also calculated that the gas-phase reaction: Hg(g) + H 2 (g) → HgH 2 (g) is endoergic by 20.8 kcal mol -1 for ground-state ( 1 S) mercury atoms .…”

Calculated spectroscopic properties of HgH2

“…0.1 %. This means that about an order of magnitude improvement has been achieved compared to the best previous work [9]. Further improvement is attained by making use of two pieces of experimental information, the ground-state rotational constant and the wavenumber of the antisymmetric stretching vibration for the most abundant isotopomer 202 HgH 2 .…”

“…Inclusion of zero-point energy reduces both values by 7.28 kJ mol -1 .The PP/CCSD(T)+SO value of 82.39 kJ mol -1 is expected to be accurate to about 1%. It may be compared with the earlier value of 86.8 kJ mol -1 by Li et al [9].…”

“…Quite recently, a three-dimensional global potential energy surface for the electronic ground state of HgH 2 (X 1 Σ g + ) was constructed from more than 13,000 energy points as calculated by the internally contracted multireference configuration interaction method (MRCI) by Li, Xie and Guo [9].…”