Spectrum of beryllium dimer in ground X 1 Σ g + state

Highlights: • The calculations of the spectrum of vibrational-rotational bound states and new metastable states of the beryllium dimer in ground $X^1{\Sigma }_g^{+}$ state important for laser spectroscopy are presented. • The upper and lower estimates of the spectrum of vibrational-rotational bound states and rotational-vibrational metastable states with complex-valued energy eigenvalues (with negative imaginary parts of the order of (${10}^{-20}÷6$) cm${}^{-1}$) in the beryllium dimer are obtained. • The existence of these metastable states is confirmed by calculating the corresponding scattering states with real-values resonance energies. The calculations of the spectrum of vibrational-rotational bound states and new metastable states of the beryllium dimer in ground $X^1{\Sigma }_g^{+}$ state important for laser spectroscopy are presented. The problem is solved using the potential energy curves from [A.V. Mitin, Chem. Phys. Lett. 682, 30 (2017)] and [M. Lesiuk et al, Chem. Theory Comput. 15, 2470 (2019)], and the authors' software package that implements the iteration Newton method and the high-accuracy finite element method. The efficiency of the proposed approach is demonstrated by the upper and lower estimates of the spectrum of vibrational-rotational bound states and, for the first time, rotational-vibrational metastable states with complex-valued energy eigenvalues (with negative imaginary parts of the order of (${10}^{-20}÷6$) cm${}^{-1}$) in the beryllium dimer. The existence of these metastable states is confirmed by calculating the corresponding scattering states with real-values resonance energies.