Short- and long-range binding of Be with Mg in the X-1 Sigma(+) ground state and in the A(1)Pi excited state

作者：Kerkines Ioannis S K^*; Nicolaides Cleanthes A

来源：Journal of Chemical Physics, 2012, 137(12): 124309.

DOI：10.1063/1.4752656

We present results of configuration-interaction (CI) computations of wavefunctions and of properties of the first two singlet states, X-1 Sigma(+) and A(1)Pi, of the, as yet unobserved, BeMg polar molecule, for internuclear distances in the range [2.5-1000] angstrom. The X-1 Sigma(+) state is very weakly bound, (D-e = 469.4 cm(-1) at R-e = 3.241 angstrom), whereas the A(1)Pi state, which correlates with the excited dissociation channel [Mg KL3s3p(1)P(o) + Be 1s(2)2s(2) S-1], is bound rather strongly (D-e = 19 394 cm(-1) (55.5 kcal/mol) at R-e = 2.385 angstrom). The X-1 Sigma(+) state supports 12 vibrational levels, for which vibrationally averaged dipole moments, <mu >(nu), were obtained, while 71 vibrational levels were found for A(1)Pi. For the level (X-1 Sigma(+)), <mu >(0) = 0.213 D. The nu '' = 7 and 8 X-1 Sigma(+) vibrational levels are found to have the highest probability to be reached via emission from the lowest lying vibrational levels of A(1)Pi. The work had a dual outcome: First, it explored consequences of different choices of the state-specific reference "Fermi-sea" space ("active" space), which is required for the construction and execution of the multiconfigurational "complete active space self-consistent field" calculations and the subsequent multi-reference CI calculations. In this context, comparisons with results on the weakly bound ground states of the homonuclear Be-2 and Mg-2 molecules were made. Second, it produced reliable data for the short-as well as the long-range parts of the potential energy curve (PEC). Such information is relevant to analyses concerning cold and ultra-cold Physics and Chemistry. For example, accurate fits to the X-1 Sigma(+) PEC, which was computed to nano-Hartree accuracy, with account for basis-set-superposition error, produced the C-6 and C-8 dispersion coefficients as 364.3 +/- 1.1 a.u. and 28 000 +/- 500 a.u., respectively. The result for C-6 is in excellent agreement with that of Derevianko et al. [At. Data Nucl. Data Tables 96, 323 (2010)], (364 +/- 4 a.u.), that was obtained in the framework of the theory of long-range interactions and many-body calculations on the constituent atoms. On the other hand, our result for C-8 differs from that of Standard and Certain [J. Chem. Phys. 83, 3002 (1985)] by about 7000 a.u.

• 出版日期2012-9-28