Sub-Doppler laser spectroscopy of the NaK molecule

Abstract

Excitation of NaK molecules in a collimated molecular beam by a single mode tunable argon laser with sub‐Doppler resolution allows selective population of definite vibrational rotational levels (v′, J′) in the D ¹Π‐state. The resultant fluorescence consists of a singlet spectrum in the 470–570 nm range and a triplet spectrum in the 625–715 nm range. The analysis of the triplet fluorescence, which consists of discrete lines and of a modulated continuum, allows the determination of the a ³Σ⁺ potential and yields very precise values for the dissociation energies in the a ³Σ⁺ and X ¹Σ⁺ states, which are measured as D_e(³Σ⁺) =204±4 cm⁻¹ and D_e(¹Σ⁺) =5269±6 cm⁻¹. For some excitation wavelengths a fluorescence spectrum with discrete lines and with a double‐modulated continuum is observed which is assigned to ’’ Condon internal diffraction’’ bands terminating close below and above the dissociation limit of the X ¹Σ⁺ state. Its relevance for the determination of the upper and lower potential curves is discussed.