%0 DATA
%A Patrick K., Tamukong
%A Mark R., Hoffmann
%A Zhendong, Li
%A Wenjian, Liu
%D 2014
%T Relativistic
GVVPT2 Multireference Perturbation Theory Description of the Electronic
States of Y_{2} and Tc_{2}
%U https://acs.figshare.com/articles/Relativistic_GVVPT2_Multireference_Perturbation_Theory_Description_of_the_Electronic_States_of_Y_sub_2_sub_and_Tc_sub_2_sub_/2319325
%R 10.1021/jp409426n.s001
%2 https://acs.figshare.com/ndownloader/files/3956962
%K 15Σ
%K ω e
%K Y 2
%K GVVPT 2 method
%K 2C
%K eV
%K spectroscopic constants Re
%K Relativistic GVVPT 2 Multireference Perturbation Theory Description
%K bond length Re
%K 11Σ
%K 31Σ
%K 19Σ
%K PEC
%K Tc 2
%K isovalent Mn 2
%K X 3Σg state
%K ground state
%K frequency ω e
%K quintet ground state
%K Tc 2The multireference
%K ground state symmetry
%K uncharacterized 21Σ g
%X The multireference generalized Van
Vleck second-order perturbation theory (GVVPT2) method is used to
describe full potential energy curves (PECs) of low-lying states of
second-row transition metal dimers Y_{2} and Tc_{2}, with scalar relativity included via the spin-free exact two-component
(sf-X2C) Hamiltonian. Chemically motivated incomplete model spaces,
of the style previously shown to describe complicated first-row transition
metal diatoms well, were used and again shown to be effective. The
studied states include the previously uncharacterized 2^{1}Σ_{g}^{+} and
3^{1}Σ_{g}^{+} PECs of Y_{2}. These states, together with 1^{1}Σ_{g}^{+}, are relevant to discussion of controversial results in the literature
that suggest dissociation asymptotes that violate the noncrossing
rule. The ground state of Y_{2} was found to be X^{5}Σ_{u}^{–} (similar to Sc_{2}) with bond length *R*_{e} = 2.80 Å, binding energy *D*_{e} = 3.12 eV, and harmonic frequency ω_{e} = 287.2 cm^{–1}, whereas the lowest 1^{1}Σ_{g}^{+} state of Y_{2} was found to lie 0.67 eV above the quintet ground state and
had spectroscopic constants *R*_{e} = 3.21
Å, *D*_{e} = 0.91 eV, and ω_{e} = 140.0 cm^{–1}. Calculations performed on
Tc_{2} include study of the previously uncharacterized relatively
low-lying 1^{5}Σ_{g}^{+} and 1^{9}Σ_{g}^{+} states (i.e., 0.70 and 1.84 eV
above 1^{1}Σ_{g}^{+}, respectively). The ground state of Tc_{2} was found to be X^{3}Σ_{g}^{–} with *R*_{e} = 2.13 Å, *D*_{e} = 3.50
eV, and ω_{e} = 336.6 cm^{–1} (for the
most stable isotope, Tc-98) whereas the lowest ^{1}Σ_{g}^{+} state, generally
accepted to be the ground state symmetry for isovalent Mn_{2} and Re_{2}, was found to lie 0.47 eV above the X^{3}Σ_{g}^{–} state of Tc_{2}. The results broaden the range of demonstrated
applicability of the GVVPT2 method.