10.1021/jp409426n.s001
Patrick K. Tamukong
Patrick K.
Tamukong
Mark R. Hoffmann
Mark R.
Hoffmann
Zhendong Li
Zhendong
Li
Wenjian Liu
Wenjian
Liu
Relativistic
GVVPT2 Multireference Perturbation Theory Description of the Electronic
States of Y<sub>2</sub> and Tc<sub>2</sub>
American Chemical Society
2014
15Σ
ω e
Y 2
GVVPT 2 method
2C
eV
spectroscopic constants Re
Relativistic GVVPT 2 Multireference Perturbation Theory Description
bond length Re
11Σ
31Σ
19Σ
PEC
Tc 2
isovalent Mn 2
X 3Σg state
ground state
frequency ω e
quintet ground state
Tc 2The multireference
ground state symmetry
uncharacterized 21Σ g
2014-02-27 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Relativistic_GVVPT2_Multireference_Perturbation_Theory_Description_of_the_Electronic_States_of_Y_sub_2_sub_and_Tc_sub_2_sub_/2319325
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<sub>2</sub> and Tc<sub>2</sub>, 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<sup>1</sup>Σ<sub>g</sub><sup>+</sup> and
3<sup>1</sup>Σ<sub>g</sub><sup>+</sup> PECs of Y<sub>2</sub>. These states, together with 1<sup>1</sup>Σ<sub>g</sub><sup>+</sup>, are relevant to discussion of controversial results in the literature
that suggest dissociation asymptotes that violate the noncrossing
rule. The ground state of Y<sub>2</sub> was found to be X<sup>5</sup>Σ<sub>u</sub><sup>–</sup> (similar to Sc<sub>2</sub>) with bond length <i>R</i><sub>e</sub> = 2.80 Å, binding energy <i>D</i><sub>e</sub> = 3.12 eV, and harmonic frequency ω<sub>e</sub> = 287.2 cm<sup>–1</sup>, whereas the lowest 1<sup>1</sup>Σ<sub>g</sub><sup>+</sup> state of Y<sub>2</sub> was found to lie 0.67 eV above the quintet ground state and
had spectroscopic constants <i>R</i><sub>e</sub> = 3.21
Å, <i>D</i><sub>e</sub> = 0.91 eV, and ω<sub>e</sub> = 140.0 cm<sup>–1</sup>. Calculations performed on
Tc<sub>2</sub> include study of the previously uncharacterized relatively
low-lying 1<sup>5</sup>Σ<sub>g</sub><sup>+</sup> and 1<sup>9</sup>Σ<sub>g</sub><sup>+</sup> states (i.e., 0.70 and 1.84 eV
above 1<sup>1</sup>Σ<sub>g</sub><sup>+</sup>, respectively). The ground state of Tc<sub>2</sub> was found to be X<sup>3</sup>Σ<sub>g</sub><sup>–</sup> with <i>R</i><sub>e</sub> = 2.13 Å, <i>D</i><sub>e</sub> = 3.50
eV, and ω<sub>e</sub> = 336.6 cm<sup>–1</sup> (for the
most stable isotope, Tc-98) whereas the lowest <sup>1</sup>Σ<sub>g</sub><sup>+</sup> state, generally
accepted to be the ground state symmetry for isovalent Mn<sub>2</sub> and Re<sub>2</sub>, was found to lie 0.47 eV above the X<sup>3</sup>Σ<sub>g</sub><sup>–</sup> state of Tc<sub>2</sub>. The results broaden the range of demonstrated
applicability of the GVVPT2 method.