Bound, even-parity<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>J</mml:mi><mml:mo>=</mml:mo><mml:mn>0</mml:mn><mml:mn/></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>J</mml:mi><mml:mo>=</mml:mo><mml:mn>2</mml:mn><mml:mn/></mml:math>spectra of Sr

Extensive new data on the even-parity, $J=0$ and $J=2$ states of Sr have been obtained using multiphoton ionization spectroscopy. Revised term values for previously observed $5s9d^{1}D_{2}$ and $^{3}D_{2}$, and $5s13d$ to $5s16d^{3}D_{2}$ states are presented in addition to term values for newly observed $^{1}S_{0}$ states up to $5s21s$, $^{1}D_{2}$ states up to $5s60d$, and $^{3}D_{2}$ states up to $5s37d$. The new data clearly show an avoided crossing between the $^{1}D_{2}$ and $^{3}D_{2}$ series near the $5s16d$ levels. A strong $J=2$ autoionizing resonance is also observed, \ensuremath{\sim}450 ${\mathrm{cm}}^{\ensuremath{-}1}$ above the first ionization limit. Multichannel quantum-defect theory (MQDT) parametrizations of the $^{1}S_{0}$, $^{1}P_{1}^{o}$, $^{1}D_{2}$, and $^{3}D_{2}$ bound-state Rydberg series are also presented, including calculated term values for these series. The MQDT analysis of the $J=2$ series in Sr differs from the earlier analysis of Ca in that both configuration interactions and recoupling between $^{1}D_{2}$ and $^{3}D_{2}$ series must be treated simultaneously. Further, it is found that all of the major perturbations of the $J=2$ bound states can be reproduced without including any interactions due to a $4{d}^{2}^{1}D_{2}$, even though $3{d}^{2}^{1}D_{2}$ is a major perturber of the $^{1}D_{2}$ series in Ca.

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