Accurate theoretical study on the ground and first-excited states of Na₂: potential energy curves, spectroscopic parameters, and vibrational energy levels

Abstract

Potential energy curves (PECs) for the ground and first-excited electronic states of Na2 are obtained by fitting the ab initio energies calculated at the MRCI(Q)/aug-cc-pVXZ (X = T, Q, 5) level of theory, which are subsequently extrapolated to the complete basis set limit. The relativistic effect and core–valence correlation are also considered. The PECs are accurate at both short and long internuclear distances with the root-mean-squared deviations being 0.72 cm−1 for Na2 [Formula: see text] and 0.36 cm−1 for Na2 [Formula: see text]. Utilizing the obtained PECs, we calculate the spectroscopic parameters, vibrational energy levels, classical turning points, inertial rotation, and centrifugal distortion constants, which are in good agreement with other theoretical and experimental work.

Accurate Ab Initio-Based Potential Energy Curve and Spectroscopic Properties of NO(X²Π) via Extrapolation to the Complete Basis Set Limit

“…From above work, the present values of the CBS/USTE (Q,5) APEF with the values of AV6Z, the deviations of R e , D e , B e , ω e , ω e χ e and α e are 0.047%, 0.445%, 0.094%, 0.697%, 0.306% and 0.173%, respectively. We can obtain the conclusion that the NO(X 2 Π) electronic state spectral parameters in the other theoretical values [38,39,37] and the experimental values [44,46] computed from the CBS/USTE(Q,5) APEF is in good consistent and showing high precision. …”

“…By the influence of the adiabatic approximation, theoretical Schrödinger equation can be written as below [37]. (16) here V(r) is the rotationless APEF, μ is the molecule reduced mass, and r is the internuclear separation of the two atom, J(J+1)· ħ 2 /2μr 2 +V(r) is the potential, so ψ ν,J (r) , J(r) are the eigenfunctions and E ν,J are the eigenvalues, J is the rotational quantum numbers and the v is the vibrational quantum numbers.…”

Ab initio calculation of the ground and first excited states of the lithium dimer

“…Alkali metals are an important class of research prototypes in the fields of physics and chemistry [1][2][3][4][5][6]. The potential energy curves (PECs) play an important role in the calculation of molecular collision reactions, and hence, a large number of theoretical and experimental studies on the PECs of the alkali metal dimers have been performed [7,8]. From the perspective of the electronic structure, the lithium dimer is the smallest homonuclear molecule in the alkali metal dimers.…”

“…Many experimental studies on the electronic states and spectroscopic constants of Li 2 have been reported. Yiannopoulou studied the S + 2 , states of 6 Li 7 Li by continuous wave perturbation facilitated OODR spectroscopy [10]. Other spectral techniques, for instance, all optical triple resonance (AOTR) etc, have also been applied to study Li 2 in experiment.…”

“…Halls et al used basis set of cc-pV5Z and the QCISD(T) method to calculate the lowest triplet excited state S + a u 3 [12]. Salihoglu et al employed two different quantum-mechanical models to obtain transition dipole moments for the 7 Li 2 S -S + + A X u g…”