Inverted Perturbation Approach Method Research Articles

Study of the 71Π u state of sodium dimer by polarisation labelling spectroscopy

Two-colour polarisation labelling experiment measuring excitation spectra of Na in the spectral range 34, 600−39, 400 cm has furnished observation of the previously unknown electronic state. The excited state is characterised by a set of Dunham coefficients describing the f parity levels up to vibrational level v = 28 and the corresponding potential energy curve is constructed by the inverted perturbation approach method. Molecular parameters determined in the fit include ± 0.03 cm, ± 0.03 cm and ± 0.001 Å.

Polarisation labelling spectroscopy of the D1Π state in Na7Li molecule

We report the first experimental observation of the D(2)1Π state in the NaLi molecule. Polarisation labelling spectroscopy technique is applied to observe transitions to all vibrational levels in this state, save v=0. The inverted perturbation approach method is used to construct a pointwise potential curve for the D state, which has a small barrier (9.3cm−1) to dissociation, located at 7.98Å.

The 4 1Σ+ electronic state of KLi molecule

The 4 1 Σ + state in KLi, characterized by a potential energy curve of irregular shape, is investigated experimentally. Spectra of the 4 1 Σ + ← X 1 Σ + band system, simplified by polarization labelling, are recorded and analyzed. The Inverted Perturbation Approach method is used to construct the exotic molecular potential of the 4 1 Σ + state. The result is compared with the prediction of theoretical calculations.

The potential energy barrier of the [formula omitted] state in KLi

The polarisation labelling spectroscopy technique has provided detailed information about the shape of the potential barrier to dissociation of the 2 Π 1 state in KLi. The potential curve of the 2 Π 1 state is constructed using the Inverted Perturbation Approach method. Our analysis shows that the barrier height is Δ E = 20.8 ± 1.0 cm −1 relative to the dissociation limit and the barrier maximum is located at R bar = 8.2 ± 0.1 Å.

The BΠ1 state of NaCs: High resolution laser induced fluorescence spectroscopy and potential construction

The lowest (1)Pi state of the NaCs molecule, the B(1)(1)Pi state, was studied using a dye laser for inducing fluorescence that was resolved by a high resolution Fourier-transform spectrometer. The presence of argon buffer gas yielded rich rotational relaxation spectra allowing to enlarge the data set for the B(1)(1)Pi state, to obtain Lambda-splittings and to reveal numerous local perturbations. 543 weakly perturbed energy levels for rotational quantum numbers from J(')=5 to 168 and vibrational quantum numbers from v(')=0 to 25, which cover about 87% of the potential well depth, were used for a direct pointwise fit of the potential energy curve applying the inverted perturbation approach method. The resulting potential reproduces the term values for v(')=0-7 with an experimental accuracy of about 0.01-0.02 cm(-1), whereas for v(')=8-25 the deviations increase due to the perturbations, going to the order of 1 cm(-1); an extrapolation is made to the dissociation asymptote.

The C 1Π u and [formula omitted] states in Li 2: Experiment and comparison with theory

The C 1Π u and 2 1 Σ u + states of lithium dimer are investigated experimentally by polarization labelling spectroscopy. The inverted perturbation approach method is used to construct the potential energy curves of both states. A very good agreement is found between the experimental potentials and those resulting from the most recent theoretical calculations.

On the 6 1Π u state of Na 2

The 6 1Π u state of sodium dimer has been observed up to v = 53 in excitation spectra of the 6 1 Π u ← X 1 Σ g + system, recorded by polarisation labelling spectroscopy technique. The Dunham coefficients are derived and the potential energy curve constructed by the inverted perturbation approach method. Equilibrium constants for the 6 1Π u state of Na 2 are: T e = 35446.06 ± 0.04 cm −1 (with respect to the minimum of the electronic ground state), Y 10 = 111.388 ± 0.019 cm −1, Y 01 = 0.112122 ± 0.000017 cm −1.

New analysis of the D(4)1Π u state of Na2 using polarization labelling spectroscopy

The D(4)1Π u state in the Na2 molecule is experimentally investigated by using the polarization labelling spectroscopy technique. The D band system is observed under rotational resolution providing information of rovibrational levels in the D state up to v,′ = 72 (that covers 85% of the potential well depth). A set of Dunham coefficients is deduced to fit the spectroscopic data and the potential curve of the D state is constructed using the Inverted Perturbation Approach method.

High resolution spectroscopy and potential determination of the (3)Π1 state of NaCs

The (3)(1)Pi state of the NaCs molecule was studied by high resolution Fourier-transform spectroscopy. The (3)(1)Pi-->X (1)Sigma(+) laser induced fluorescence was excited by an Ar(+) ion laser or by a single-mode frequency-doubled cw Nd:YAG laser. The presence of argon buffer gas yielded rich rotational relaxation spectra allowing to enlarge the data set for the (3)(1)Pi state term values, as well as to observe Lambda splittings in a wide range of vibrational (v(')) and rotational (J(')) quantum numbers. The data field includes about 820 energy levels of (3)(1)Pi NaCs in the range from v(')=0 to 37 and from J(')=3 to 190, which corresponds to ca. 95% of the potential well depth. Direct fit of the potential energy curve to the level energies is realized using the inverted perturbation approach method; a set of Dunham coefficients is also presented.

New observation and analysis of the E(4) 1Σ + state in NaLi

Polarization labeling spectroscopy is applied to study the excited E(4) 1Σ + state of NaLi in the energy range 25 850–27 750 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 D1Π state of the NaRb molecule

We present a detailed experimental study of the D1Π state of the NaRb molecule by means of Fourier transform spectroscopy of laser induced fluorescence. The entire data field for the D1Π state of Na85Rb and Na87Rb consists of rovibrational levels with v′=0-39 and J′=1-200. The data were incorporated into a direct fit of a single potential energy curve to the level energies using the Inverted Perturbation Approach method. The D1Π state q factors, which describe the Λ-doubling, have been obtained in a wide range of rotational and vibrational quantum numbers. Analysis revealed several perturbation regions in the D1Π state.

Accurate characterisation of the C(3)1Σ+ state of the NaRb molecule

We present a first detailed experimental study of the C(3)1Σ+ state of the NaRb molecule converging to the Na(3p) + Rb(5s) states of separated atoms. Two different high resolution spectroscopic methods have been applied: the Fourier transform spectroscopy of laser induced fluorescence and the V-type optical-optical double resonance polarization labeling spectroscopy. The entire data field for the C1Σ+ state of Na85Rb and Na87Rb consists of rovibrational levels with v'=0–64 and J'=4–123. The data were incorporated into a direct fit of a single potential energy curve to the level energies using the Inverted Perturbation Approach method. As the experimental data extend to the “shelf" region of the potential at large internuclear separations of 8.5 A, the C state's suitability for photoassociation yielding cold heteronuclear NaRb is discussed.

Experimental characterisation of the double minimum 6 1Σ + state in NaRb

Polarisation labelling spectroscopy technique was employed to study the double minimum 6 1Σ + state of NaRb molecule. Six lines of an argon ion laser were used to label rovibronic levels in the electronic ground state and the excitation spectra in the 6 1Σ + ← X 1Σ + band system were recorded in the spectral range 24 100–26 500 cm −1. Energies of 901 rovibronic levels of the inner well of the 6 1Σ + state were determined for two isotopomers of NaRb. The potential curve of the 6 1Σ + state was constructed using the inverted perturbation approach method.

A regularized inverted perturbation approach method: potential energy curve of the 4 (1)Sigma(u) (+) state in Na(2).

We describe a modification of the inverted perturbation approach method allowing to construct physically sensible potential energy curves for electronic states of diatomic molecules even when some parts of the potential are not adequately characterized by the experimental data. The method is based on a simple regularization procedure, imposing an additional constraint on the constructed potential curve. In the present work it is applied to the double minimum 4 (1)Sigma(u) (+) state of Na(2), observed experimentally by polarization labeling spectroscopy technique.

Potential curve of the 4 1Σ + state of NaK by polarisation labelling spectroscopy

The 4 1Σ + state of NaK molecule has been observed for the first time and studied by polarisation labelling spectroscopy technique. A total of 1567 rovibronic levels in this state were measured with an accuracy better than 0.1 cm −1. The inverted perturbation approach method was used to construct the potential energy curve of the 4 1Σ + state. The irregular shape of the potential confirms earlier theoretical predictions.

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

Polarization labelling spectroscopy is applied to study the excited E 1Σ + 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 T e, ω e and R e are found to be 26 474.82(4), 180.3(2) cm −1 and 3.343(1) Å, respectively.

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.

Construction of potential curves for diatomic molecular states by the IPA method

A program package is presented which utilizes the Inverted Perturbation Approach (IPA) method for construction of potential energy curves of 1Σ and 1Π states of diatomic molecules directly from the experimental data. In most cases using the constructed IPA potential one can reproduce the experimental energy levels within the accuracy of measurement. The package is successfully tested in case of double minimum potential where the traditional RKR method is not applicable.