Electronic structure of the CdKr lowest Rydberg state determined from laser-excitation spectra using supersonic beam and double optical resonance methods

Abstract

The lowest $E\phantom{\rule{0.3em}{0ex}}^{3}\ensuremath{\sum}^{+}(6\phantom{\rule{0.3em}{0ex}}^{3}S_{1})$ Rydberg state of the CdKr van der Waals complex was investigated using supersonic-expansion beam and the optical-optical double-resonance methods. Well-defined vibrational levels $A\phantom{\rule{0.3em}{0ex}}^{3}0_{{v}^{\ensuremath{''}}=9}^{+}(^{3}\ensuremath{\Pi})$ and $B\phantom{\rule{0.3em}{0ex}}^{3}1_{{v}^{\ensuremath{''}}=1}^{+}(^{3}\ensuremath{\sum}^{+})$ were used as intermediate states being excited from the $X\phantom{\rule{0.3em}{0ex}}^{1}0^{+}(^{1}\ensuremath{\sum}^{+})$ ground state. Two types of bound-bound excitation spectra of the $E\phantom{\rule{0.3em}{0ex}}^{3}\ensuremath{\sum}^{+}\ensuremath{\leftarrow}A\phantom{\rule{0.3em}{0ex}}^{3}0^{+}$ and $E\phantom{\rule{0.3em}{0ex}}^{3}\ensuremath{\sum}^{+}\ensuremath{\leftarrow}B\phantom{\rule{0.3em}{0ex}}^{3}1$ transitions were observed and recorded. The analyses of the spectra suggest an existence of two, well-defined minima in the $E\phantom{\rule{0.3em}{0ex}}^{3}\ensuremath{\sum}^{+}$-state potential-energy (PE) curve: an inner PE well ${E}_{1}$ with ${D}_{\mathrm{e}}^{\ensuremath{'}}({E}_{1})=1656\phantom{\rule{0.3em}{0ex}}{\text{cm}}^{\ensuremath{-}1}$ and an outer well ${E}_{2}$ with ${D}_{\mathrm{e}}^{\ensuremath{'}}({E}_{2})=27\phantom{\rule{0.3em}{0ex}}{\text{cm}}^{\ensuremath{-}1}$, separated from each other by a positive-energy barrier. Combination of bound-bound spectra excited from different intermediate states enabled probing of the $E\phantom{\rule{0.3em}{0ex}}^{3}\ensuremath{\sum}^{+}$-state potential in a relatively large range of internuclear separations $R$ and hence it led to a complete determination of spectroscopical parameters of the $E\phantom{\rule{0.3em}{0ex}}^{3}\ensuremath{\sum}^{+}$-state PE curve. The height of the barrier and its approximate location were also determined. The experimental results of this investigation coincide well with the results of ab initio calculation of Czuchaj and co-workers [Chem. Phys. 248, 1 (1999); Theor. Chem. Acc. 105, 219 (2001)].