INVESTIGATION OF $L$-UNCOUPLING AND $\Lambda$-DOUBLING IN THE RYDBERG STATES OF THE SODIUM DIMER
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Date
2007
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Publisher
Ohio State University
Abstract
The phenomenon of electronic orbital angular momentum $L$ uncoupled from its internuclear axis has been observed in the sodium dimer using high resolution cw optical-optical double resonance spectroscopy. When $L$-uncoupling occurs, the degeneracy of $\Lambda$-doubling is removed. In our experiment, the intermediate $B\,^1\Pi_u$ state of Na$_2$ is excited from the thermally populated ground $X\,^1\Sigma^+_g$ state by a single line Ar$^+$ laser. Then, a single-mode dye laser is used to probe the Rydberg states from the intermediate state. The signals are detected by monitoring the UV fluorescence from the triplet \emph{gerade} states back to the $a\,^3\Sigma^+_u$ state via collision energy transfer. Under our experimental resolution, the splitting of $L$-uncoupling and $\Lambda$-doubling in both the $5\,^1\Delta_g$, $5\,^1\Pi_g$ states of Na$_2$ can be measured.Total of 136 rovibronic levels with $e/f$ parities have been assigned to the $5\,^1\Delta_g$ state. The $\Lambda$-splitting constants deduced from these data are : $q_0$=\,$0.376(90)\times10^{-4}$\,cm$^{-1}$ , $q_v$=\,$0.114(6)\times10^{-4}$\,cm$^{-1}$ , $\mu$=\, $ 0.76(33)\times10^{-8}$\,cm$^{-1}$. In general, the $\Lambda$-splitting of the $\Delta$ states is considerably smaller than that of the $\Pi$ states. However, the first order splitting constants $q_{0}$ and $q_v$ reported here are larger than those in the $B\,^1\Pi_u$ state. This is due to the $L$-uncoupling of the Rydberg states. Total of 230 rovibrational levels are assigned to the Na$_2$ $5\,^1\Pi_g$ state, and the following are its correspondent $\Lambda$-splitting constants : $q_0$=\,$0.1758320898(0.017)\times10^{-3}$\,cm$^{-1}$ , $q_v$=\,$-0.7124318162(0.071)\times10^{-5}$\,cm$^{-1}$ , $\mu$=\,$ -0.9608208561(0.8)\times10^{-8}$\,cm$^{-1}$. The splitting of $\Lambda$-doubling increases quadratically with the rotational quantum number $J$ and weakly depends on the vibrational quantum number $v$. These splitting constants are much larger than those in the Na$_2$ $B\,^1\Pi_u$ state. This indicates that the splitting of $\Lambda$-doubling in the $5\,^1\Pi_g$ state is affected by both the perturbations by adjacent $\Sigma$ states and the $L$-uncoupling. (grand no. NSC-95-2112-M-012-MY3).
Description
Author Institution: Department of Physics, National Cheng-Kung University, Tainan 70101,Taiwan(R.O.C.); Department of Chemistry, National Cheng-Kung University, Tainan 70101, Taiwan(R.O.C.); Department of Physics, National Cheng-Kung University, Tainan 70101, Taiwan(R.O.C.)