NAK-LAMBDA DOUBLING AND PERMANENT ELECTRIC DIPOLES IN LOW-LYING (1)PISTATES - EXPERIMENT AND THEORY

The paper presents Lambda splittings and q factors in the NaK D (II)-I -1 state, directly measured from the electric radio-frequency-optical double resonance (RF-ODR) in laser-induced fluorescence (LIF) for a nu mber of vibrational states v = 1-22 with definite rotational levels J between 7 and 46. Permanent electric dipole moment values (d) have bee n obtained by measuring in LIF spectra the relative intensities of ''f orbidden'' lines caused by de Stark effect induced elf mixing in the ( II)-I-1 state, with their subsequent processing, which allowed us to o btain the q/d ratio. A possible influence of the hyperfine structure o n the RF-ODR signal and relative intensities has been calculated, show ing that this influence can be neglected. The q(v) values exhibited a decrease from q(1) = 1.529x10(-5) cm(-1) to q(22) = 1.171x10(-5) cm(-1 ), which has been explained by an increase of the difference potential between D (II)-I-1 and C (1)Sigma(+) states with internuclear distanc e (R); the respective L-uncoupling matrix element was evaluated as 1.8 7. It was shown, both by semiempirical treatment and population analys is of ab initio molecular wave functions, that considerable pi d and s igma d configuration admixtures are present in the D (II)-I-1 and the C (1)Sigma(+) states. For the B (II)-I-1 state, it was demonstrated th at Lambda doubling is caused by two competing perturbers (A (1)Sigma() and C (1)Sigma(+)), yielding q factors of similar to-2 x 10(-6) cm(- 1), in agreement with high-resolution spectroscopy data given in the L iterature; single-configuration approximation is valid for interacting B (II)-I-1(sigma 3s(Na), pi 4p(K))similar to A (1)Sigma(+)(sigma 3s(N a),a4p(K)) states. The measured d(v) values, which varied from 6.6 to 4.6 D, have been used to obtain the empirical D (II)-I-1. state d(R) f unction for R = 6-12 a.u. by means of an improved instability-free inv ersion procedure exploiting a special functional form. Two independent series of ab initio all-electron calculations of d(R) and d(v) have b een performed for the D (II)-I-1. and B (II)-I-1 states of NaK. First, d values were computed as expectation values of the electric dipole o perator with conventional multireference configuration-interaction wav e functions. Second, the finite-field (FF) technique, combined with a multipartitioning perturbation theory (MPPT) treatment of electronic e igenstates, was applied for the calculation of d(R) functions. The FF- MPPT calculations showed excellent agreement with experimental D (II)- I-1 d(v) values obtained in the present work, as well as the proximity to experimental B (II)-I-1 d(v) values given in the literature, thus showing that, as distinct from the ground state, it is important to ac count correctly for effective interactions of valence electrons arisin g from core-valence correlations, which could not be done properly wit h previously used pseudopotential techniques. The experimental d and a values dropping out from a smooth v dependence have been considered a s perturbed by D (II)-I-1 similar to d (II)-I-3 interaction and exploi ted to evaluate respective d(1) and c(1) values for the perturbing d ( II)-I-3 state.