Photoelectron and threshold photoelectron valence spectra of pyridine

The pyridine molecule has been examined by the means of photoelectron and threshold photoelectron spectroscopies. Ionization energies were determined for both outer and inner valence orbitals and new adiabatic values were also resolved. Vibronic structure associated with several states was assigned mainly to be due to C-C stretches and ring bends. Additionally a Rydberg state converging to 7b2 state was ascribed. The data shown here are in a good agreement with previous results and brings some new insights into the electronic structure of this biologically and astrochemically relevant and important molecule

3dnd J = 4,5 autoionizing levels in Ca: laser optogalvanic spectroscopy and theoretical analysis

We report the even parity J=4,5 autoionizing spectra of calcium below the 3d threshold, investigated by two-step laser excitation from the 3d4s metastables through the 3d4p $^3{\rm F}_{3,4}$, $^1{\rm F}_3$ intermediate states and subsequent optogalvanic detection. The 3d4s states are populated by electronic collisions in a d.c. glow discharge sustained in a Ca heat-pipe. More than a hundred resonant transitions have been measured with an accuracy of $\sim 0.2 {\rm cm}^{-1}$ for the narrow ones using standard laser calibration techniques. The high lying levels are assigned to all expected $3{\rm d}n{\rm d} J=4,5$ autoionizing series. Moreover, some $3{\rm d}n{\rm g} J=4,5$ levels are observed. The theoretical interpretation is achieved by a combination of the nearly ab initio eigenchannel R-matrix and multichannel quantum-defect (MQDT) methods as well as by an empirical determination of the MQDT parameters in the phase-shifted formulation. Theoretical energy level positions and excitation profiles are compared with the experimental data confirming the identification of the observed structures. Strong mixing between $3{\rm d}n{\rm d} J=4$ series is found, while the $3{\rm d}n{\rm g}$ ones do not couple with the $3{\rm d}n{\rm d}$ series. Further insight into the strong channel mixing in the studied energy range is provided by a comprehensive review of the excitation profiles in the vicinity of the 4p5p $^3{\rm D}_3$ perturber as obtained from a number of intermediate levels used in the present and in earlier experiments. Systematic electron correlation trends for $N{\rm d}n{\rm d} J=4$ series of ${\rm Ca} (N=3)$, ${\rm Sr} (N=4)$ and ${\rm Ba} (N=5)$ are discussed

Experimental and theoretical analysis of the 5pnpJ=0

The even parity 5 p n p J=0, 1 and 2 doubly excited autoionizing states of strontium were investigated both experimentally and theoretically. Sr atoms in an atomic beam were excited through the two-step Isolated Core Excitation (ICE) scheme $5s^2$ $^1{\rm S}_0 {-}{\lambda_1}$ $\rightarrow 5sn' p ^1{\rm P}_1 (n'=12{-}16) {-}{\lambda_2}$ $\rightarrow [5p_{3/2}np]_J$. The final ICE transition probes the $[5p_{3/2}np]_J$ resonances. However, the $[5p_{1/2}np]_J$ series below the $5p_{1/2}$ threshold were excited also due to their mixing with the $[5p_{3/2}np]_J$ perturbers. An extended energy region was covered below and above the $5p_{1/2}$ ionization limit by saturating the central ICE lobe and recording as many as possible "red"and "blue"secondary lobes. J identification was achieved by using mutually parallel and perpendicular linear polarizations of the laser beams. The ICE spectra were compared to those obtained by employing a two-step excitation scheme using the bound $4d5p ^1{\rm P}_1$ valence state as an intermediate one. Final identification for very complex structures was achieved after comparison with theoretical energy level positions and excitation profiles produced by the R-matrix method combined with the multichannel quantum defect theory (MQDT) method. The agreement between theoretical and observed structures is quite satisfactory