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Accurate ab initio calculations of the potential energy curves (PEC) of the electronic states of the neutral S 2 molecule and the S 2 − negative ion, correlating to the boundreveal that the depletion of the J = 7/2 component of the S 2 − (1 4 g ) state occurs mainly via weak interactions with the electron continuum wave.This quartet is found to possess several long-lived rovibrational levels which are located below the S 2 (c 1 u − ) parent neutral state. Those levels may be populated, at least, during low-energy collisions between S − ( 2 P u ) and S( 3 P g ).

Ab initio theory with VQZ (valence quadruple zeta) basis set at the CASSCF (complete active space self consistent field) level was used to predict the shape of the potential energy functions of the HS 2 radical and its cation HS 2 + . In each case, calculations have been carried out for the lowest electronic states for linear and bent geometries. For HS 2 , the X 2 A" ground electronic state correlates in linear geometry with a 2 II state. It leads with the A 2 A' state to a bent-bent Renner-Teller system. For HS 2 + , the ground electronic state is X 3 A" and it correlates with a 3 Σstate. The cuts of potential energy functions along the internal coordinates for all the electronic states correlating with the lowest dissociation asymptotes have been taken into account. This will be very helpful for understanding the reactivity of the S, S + , H, and H + atomic systems with the SH, SH + , S 2 and S 2 + diatomic species to form the triatomic HS 2 and HS 2 + systems, which play a key role as intermediates in sulfur-bearing species reactions. Using perturbation treatment, spectroscopic data for the ground electronic states of both systems have been calculated and compared well with previous experimental results.We first studied the resonant photoionization of helium-like ions, such as C4+, N5+, and O6+, and determined the wave functions, the excitation energies, and the partial and total widths of the autoionizing states of these ions lying under the n = 3 thresholds of the residual ion. For more detailed analysis of the theory, and a better comprehension of the internal dynamics of atomic resonances and electronic phenomena of correlation, we extended these calculations to other helium-like ions, under higher thresholds (n = 4 and 5) of the hydrogen ions H -, and of Li+, C4+, N5+, and O6+. We were also interested in oscillator strengths. These parameters are important for interpreting the spectra and diagnosing astrophysical and laboratory plasmas, as well as for analyzing the spectra coming from space and determining the composition and relative abundance from the various elements of the stellar and interstellar environment. We sought a better comprehension of the coupling between autoionizing and continuum states and of the phenomena of electronic correlations. We used the method of diagonalization that has been used below the n = 2 threshold of the residual ion. The results are important for astrophysicists and physicists studying matter-radiation interaction and for the invention of new laser systems. We also measured laser-induced chlorophyll fluorescence (LICF) emission spectra of the leaves of some tropical plants using a compact fiber-optic fluorosensor with a continuous-wave violet diode laser as the exciting source and an integrated digital spectrometer to analyze the state of stress of the plants. 201