Excited-state spectroscopy of $Rb_2$ and KRb by resonance enhanced two photon ionization in a supersonic molecular beam

Abstract

Resonance enhanced two-photon ionization spectroscopy of $Rb_{2}$: 500-nm system. Resonance enhanced two-photon ionization (RE2PI) study in a pulsed molecular beam identified new $2 ^{3}∏_{u}(0_{u}^{+}, 1_{u}) - X ^{1}∑_{g}^{+}(0_{g}^{+})$ transitions of $Rb_{2}$. These transitions are spin-forbidden and borrow transition moments from other allowed transitions. These two borrowed perpendicular and parallel transition moments interfere each other and which is caused by heterogeneous perturbation connects the two upper states. Interference pattern is observed in the relatively weak $1_{u}$ subband with very sharp contrast, which is interference-induced rotational-branch intensity anomaly. In the $1_{u}$ subband, the intensity of R-branch (ΔJ = +1) rotational lines is very enhanced while that of P-branch (ΔJ = -1) rotational lines almost disappears. Resonance enhanced two-photon ionization spectroscopy of $Rb_{2}$: 475-nm system. Perturbations in the $Rb_{2}$ 475-nm system were studied by resonance enhanced two-photon ionization in a supersonic molecular beam. The rotational structures of the $2^{1}∏_{u}$, $2 ^{1}∑_{u}^{+}$ and extra bands were analyzed. Vibrational-level dependence of perturbed molecular constants reveals that the perturbation is strongest in the v` = 7 and 8 levels of the $2 ^{1}∏_{u}$ state. The $2 ^{1}∏_{u}$ $v` = 5 - 8$ bands are accompanied with five strong extra bands. The rotational structures of these extra bands show that their electronic symmetries are same with that of the $2 ^{1}∏_{u}$ state. Therefore, the perturbation between the $2 ^{1}∏_{u}$ and the upper electronic states of the extra bands is through a homogeneous spin-orbit coupling. This perturbation enables the $2 ^{1}∏_{u}$ state to be an intensity source of dark states of $2^{3}∏_{u}(1_{u})$ and $3^{3}∑_{u}^{+}(1_{u})$ states in this spectral region. To assign the upper electronic states of the extra bands we compared observed rotational and vibrational properties with...