Calculation of the singlet-triplet magnetic and electro-quadrupole transitions intensity for Ge2 molecule

Intensity of the parity-forbidden singlet-triplet (S-T) transitions of the Ge-2 molecule in the near IR region has been studied by the multi-reference configuration interaction (MRCI) approach with spin-orbit coupling (SOC). Intensity of the b(1) Sigma(+)(g) - X-3 Sigma(-)(g,Ms=1) sub-band is mainly dominated by the spin angular momentum term in the magnetic-dipole transition moment, which arises from the spin current inside the zero-field split sublevels of the ground X-3 Sigma(-)(g) state. The Einstein coefficients corresponding to vibronic v' - v '' bands 0-(2 similar to 7), 1-(4 similar to 7), 2-(6 similar to 7), 3-7 of the b(1) Sigma(+)(g)- X-3 Sigma(-)(g,Ms=1) transition are in the range of 0.304- 0.463 s(-1); these bands could be detected since they are not overlapped by the allowed rovibronic systems. The magnetic-dipole a(1) Delta(g) - X-3 Sigma(-)(g,Ms=1) is only defined by the orbital angular momentum term and the band intensity is not sufficient for observation. The electric-quadrupole a(1) Delta(g) - b(1) Sigma(+)(g) and a(1) Delta(g) - X-3 Sigma(-)(g,Ms=0) transitions have also been calculated to be negligible. The triply forbidden electro-dipole transitions in the IR spectrum of the Ge-2 throws new light on this little known domain of diatomic molecular spectroscopy. [GRAPHICS]