The C(2)1Πu state in Rb2. Observation and deperturbation.

We report a systematic study of the C(2)1Πuelectronic state in rubidium dimer, observed in polarization labelling spectroscopy experiment through the C ← X1Σg+ transitions recorded under rotational resolution in two isotopologues 85Rb2 and 85Rb87Rb. Regularity of the vibrational progressions was distorted by numerous interactions with the surrounding 21Σu+, 23Πuand 33Σu+states. Deperturbation was performed by coupled-channels analysis taking into account spin-orbit and rotational interactions. Potential energy curves and parameters describing the off-diagonal matrix elements were determined as functions of internuclear distance. About 3000 line frequencies from the present study are reproduced with a standard deviation of 0.07 cm-1, in agreement with the experimental accuracy. Along with this, the model is consistent with all high resolution experimental data on the involved electronic states, available in the literature.

The B(1)Π and D(1)Π states of LiRb.

We studied the molecule LiRb in the gas phase with high resolution by Fourier-transform spectroscopy of laser induced fluorescence. The spectra were assigned to transitions between the ground state X(1)Σ(+) and B(1)Π or D(1)Π states and showed perturbations. For levels with e symmetry the coupling to the nearby state C(1)Σ(+) was included in the analysis by means of coupled channel calculations. The evaluation gives potential energy curves for all three electronic states and the coupling functions for B-C coupling, which are related to the expectation value of the electronic orbital angular momentum operator L(+) or L(-). The same coupling between C and D states is considered, but is not yet as fixed as in the case B-C because of lack of data. The model was extended to include the Λ-doubling by distant electronic states through effective q-parameters, but their interpretation is incomplete because of several possible perturbing states and too few data.

Spectroscopic study of the 2(2)Σ+ and the 4(2)Σ+ excited states of LiCa.

The 2(2)Σ(+) and 4(2)Σ(+) excited states of (7)Li(40)Ca have been studied by high resolution Fourier-transform spectroscopy. The data on the lower state, 2(2)Σ(+), were obtained by analyzing the rotationally resolved spectra of the thermal emission of LiCa in the 2(2)Σ(+) → X(2)Σ(+) band around 9500 cm(-1). These data contained transitions mainly from v' = 0 and 1 for N' up to 92 and allowed us to derive molecular parameters describing the potential curve of the state close to its minimum. The dataset on the second state, 4(2)Σ(+), is much larger and comes from a laser-induced fluorescence experiment. The levels were excited by a single mode dye laser and the 4(2)Σ(+) → X(2)Σ(+) fluorescence was recorded through a Fourier-transform spectrometer. For both states potential energy curves and Dunham coefficients were derived and the spin-rotation structure was evaluated. The results are compared with theoretical and experimental data from the literature.

Fitting potential energy curves for diatomic molecules using experimental line intensities.

The existing routines for construction of experimental potential energy curves for diatomic molecules are based mainly on transition frequencies while the line intensities are seldom used. Some of the reasons for this are experimental: the line intensities are usually measured with much higher uncertainty. Other are numerical and the main problem is to fix the sign of the overlap integrals since the line intensity depends on their square. In this contribution a simple approach is proposed for solving this problem.

The X2Σ+ state of LiCa studied by Fourier-transform spectroscopy.

The paper reports on a successful observation of high resolution Fourier transform spectra of LiCa. The fine structure of the ground state was observed and attributed to effective spin-rotation interaction. The experimental observations are described by two models using potential energy curves. One of them takes into account the fine structure splitting by means of effective constants, the other by means of a R dependent function γ(R), built in the radial Schrödinger equation. Ab initio calculations were performed for γ(R) which comes close to the experimental function.

The X 1Σ+ state of LiRb studied by Fourier-transform spectroscopy.

We report on the first experimental observation of the ground electronic state of the LiRb molecule at high resolution. A large body of experimental data was collected which led to an accurate potential energy curve for this state. Transitions to the lowest triplet state were also observed, but these data are rather fragmentary and allow only a first attempt for the description of this state. Both potentials were used for evaluating published Feshbach resonances of this molecule. We compare the results of this study with those of the related LiK and LiCs molecules.