Theoretical calculations for the ground state and for 83 excited states of the Na2 molecule are presented in the framework of two independent approaches. The electron–core interaction is represented either by a pseudopotential or by a model potential, and a core polarization potential is introduced in both cases. The basis set contains either Gaussian orbitals or two‐center generalized Slater orbitals. The two methods appear to give similar results, one being more accurate for the ground and first excited states, the other being better adapted to the intermediate Rydberg states. A very good agreement is obtained with the experimental spectroscopic constants determined for 26 states, the mean deviation being ΔRe=0.05a0, Δωe=0.86 cm−1, and ΔDe=57 cm−1.

Potential curves for the ground and excited states of the Na2 molecule up to the (3s+5p) dissociation limit: Results of two different effective potential calculations

Assessment of biodiversity of pollinators on the landscape scale or estimation of fluxes of disease-transmitting biting midges constitutes a major technical challenge today. We have developed a laser-radar system for field entomology based on the so called Scheimpflug principle and a continuouswave laser. The sample-rate of this method is unconstrained by the round-trip time of the light, and the method allows assessment of the fast oscillatory insect wing-beats and harmonics over kilometers range, e.g., for species identification and relating abundances to the topography. Whereas range resolution in conventional lidars is limited by the pulse duration, systems of the Scheimpflug type are limited by the diffraction of the telescopes. However, in the case of sparse occurrence of the atmospheric insects, where the optical cross-section oscillates, estimation of the range and spacing between individuals with a precision beyond the diffraction limit is now demonstrated. This enables studies of insect interaction processes in-situ.

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Super Resolution Laser Radar with Blinking Atmospheric Particles - Application to Interacting Flying Insects

Publisher Summary This chapter presents an account of research into fundamental questions, spanning roughly the past decade, and provides continuity from earlier reviews of collisional ionization. The chapter discusses progress along three principal lines: (1) experimental investigation of the fundamental questions, (2) the calculation of molecular potential curves required for the interpretation of experiments, and (3) a review of theoretical approaches developed to grapple with the physics of electron bound-free coupling in heavy particle associative and dissociative processes. The chapter explains the problem of molecular potentials and dynamics of associative ionization. The treatment of associative ionization necessitates knowledge of accurate potential curves and dynamical couplings characterizing the quasi-molecule formed during the collision. Dynamics of associative ionization reviews and classifies the theoretical approaches. It assumes that the basic molecular data, the potential curves and couplings responsible for the ionization process are either known from first principles or have been parametrically fit to experimental results.

Associative Ionization: Experiments, Potentials, And Dynamics

The excited potential curves of Na2 are computed up to the states dissociating into Na(3s)+Na(4d) by a two-electron model potential method which uses an expansion on screened two-centre orbitals. The agreement between the computed excitation energies and the experimental determination is better than 200 cm-1. A good agreement is also found with previous calculations of Jeung (1983,1987) up to the 3s+5s dissociation limit, but not with previous calculations of Jeung and Ross (1988) for the states dissociating into 3p+3p. The analysis of the results in terms of molecular quantum defects reveals some avoided crossings characteristic of two-electron effects.

Model potential calculations for the intermediate Rydberg states of Na2: adiabatic potential curves and molecular quantum defects

An optical spectroscopy apparatus and method for measurement of species concentration, number density, or column density comprising emitting light from a laser light source, receiving light via a fixed length optical path from the source and containing a species to be detected, receiving light via a detector at an end of the path, determining one or more of species concentration, number density, and column density via signal processing electronics connected to the detector, and switching between a plurality of operational modes measuring a same absorption feature of the species depending on measured absorbance.

Gas measurement over extreme dynamic range of concentrations

Doppler-free saturation spectroscopy in the regime of strong pumping intensities and optically thick atomic samples is investigated experimentally and theoretically. It is shown that a very high signal-to-background ratio can be obtained and, at the same time, subnatural linewidths can be reached. Further contrast and linewidth improvements can be attained by supplementing the primary depleted pumping beam with a second pumping beam. By using the signal beam from a first setup as the pumping beam for a second identical arrangement, extreme values for contrast and linewidth should be attainable.

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Saturation spectroscopy for optically thick atomic samples

Fluorescence spectroscopy is used as an aid in the identification of two-photon transitions in Na2. Several methods are introduced and used to identify the transitions and analyze the spectra. By using these methods, the upper-level rotational quantum number, energy, and electronic character may be determined without any assumptions about the state to which the upper level belongs. Twenty-nine two-photon transitions were observed and analyzed. A Dunham expansion for the energy levels allowed 18 of the 29 to be associated with the Σ1g+ (3s+5s) state. They were used to calculate new values of the Dunham coefficients for that state. These were in close agreement with values obtained in polarization-labeling experiments.

W. M. Du

Papers

Saturation spectroscopy for optically thick atomic samples

Constants of the 5s 1 Σg+ state of Na 2 from two-photon spectroscopy