A. Pashov

The Li2 F 1Σg+ “shelf” state: Accurate potential energy curve based on the inverted perturbation approach

We report an accurate inverted perturbation approach (IPA) potential energy curve for the “shelf” Fu200a1Σg+ state in Li2 which reproduces positions of the experimental energy levels available in the literature for all three isotopomers 7Li2, 6Li7Li, and 6Li2 with a standard deviation of 0.11 cm−1. Our analysis significantly improves the shape of the recently reported Rydberg–Klein–Rees (RKR) potential curve of the Fu200a1Σg+ state [Antonova et al., J. Chem. Phys. 112, 7080 (2000)] and provides evidence for the existence of a shallow minimum in the shelf region. Using our IPA potential curve we were able to localize and identify some local perturbations in the spectra, as well as to correct the assignment of several spectral lines previously observed experimentally.

On the X 1∑+ state of KLi

Laser-induced fluorescence spectra of the B–X system of 39K7Li, recorded on a Fourier transform interferometer, have allowed 47 vibrational levels of the electronic ground state to be observed. The ground state energies have been fitted to a Dunham polynomial expansion, and also directly to a numerical potential curve. Both fits reproduce the data to within the experimental accuracy of measurement (0.005 cm−1).

The B1Π and C1Σ+ states of KLi

Abstract The polarization labelling spectroscopy technique is used to study the B 1 Π ← X 1 Σ + and C 1 Σ + ← X 1 Σ + band systems of the KLi molecule. Accurate molecular constants are derived for the B and C states from a Dunham expansion. For the B 1 Π state our analysis covers more than 99% of the potential well depth and provides a precise value for its dissociation energy. This also allows dissociation energies of the ground X 1 Σ + state and excited C 1 Σ + state to be determined.

The E1Σg+ state of lithium dimer revised

This article describes the use of the inverted perturbation approach method for construction of an accurate potential energy curve of the E1Σg+ “shelf” state in Li2. Contrary to previous reports the applied method provides a potential curve free of unphysical oscillations and reproduces energies of all the levels known from previous experiments. Our results confirm the possibility of describing the E state within the Born–Oppenheimer approximation.

Spectroscopic study of the E(4)1Σ+ state in NaLi

Polarization labelling spectroscopy is applied to study the excited E1sigma+ state of NaLi in the energy range 26,500-28,000 cm(-1) above the bottom of the ground state. The potential curve of the E state is constructed using the Inverted Perturbation Approach method. The values of Te, omega(e) and Re are found to be 26,474.82(4), 180.3(2) cm(-1) and 3.343(1) A, respectively.

The B1Π and D1Π 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.

Potential energies of the 4 and 5 states of NaK by polarization labelling spectroscopy and by ab initio calculations

Abstract The 41Π and 51Π states of the NaK molecule have been investigated experimentally by polarization labelling spectroscopy technique and theoretically within the framework of the ab initio pseudopotential method. A very good agreement has been obtained between the calculated potential curves and those determined from experimental observations.

Spectroscopic study of the 22Σ+ and the 42Σ+ 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.

An improved description of the double minimum 6 1Σ+ state of NaK by an IPA potential energy curve

The inverted perturbation approach (IPA) method is used to construct the potential energy curve of the double minimum 6xa01Σ+ state of NaK. The IPA potential makes it possible to reproduce the experimental energies of 1032 rovibrational levels situated both in the inner well and above the internal maximum of the potential.

Laser and Fourier transform spectroscopy of 7Li88Sr

LiSr was produced in a heat-pipe oven and its thermal emission spectrum around 9300 cm−1 was recorded by a high resolution Fourier transform spectrometer. In addition, selected lines of the spectrum of deeply bound vibrational levels of the and states were studied using laser excitation to facilitate the assignment of the lines. The ground state could be described for to 2, up to 105 and the state for up to . For both states, Dunham coefficients, spin–rotation parameters and potential energy curves were evaluated. A coupling of the state to the state was observed, allowing a local description with Dunham coefficients of the state and an approximate evaluation of the coupling strength.