Molecules Rydberg states

Molecule Rydberg state Rydberg orbital A (atom)0 AR(obs) Valence state Ay(obs)... 

Three-photon absorption has also been observed by multiphoton ionization, giving Rydberg states of atoms or molecules [36]. Such states usually require vacuum ultraviolet teclmiques for one-photon spectra, but can be done with a visible or near-ultraviolet laser by tluee-photon absorption. 

Merkt F 1997 Molecules in high Rydberg states Ann. Rev. Phys. Chem. 48 675-709... 

Our best estimation for the vertical excitation energies for states of A, symmetry are reported in Table 12. They correspond to a ground state calculated at CI( 6) level using orbitals optimized for the neutral molecule with the MCSCF/SD expansion, and excited Rydberg states calculated at the level using orbitals optimized for the positive ion... 

Vertical excitation energies to states of B symmetry, calculated at the level using the orbitals optimized for the neutral molecule with the MCSCF/6422 expansion, are reported Table 12. The I Bi valence state and 2 B (3p) Rydberg state of C3H2 are respectively 5.2 eV and 7.5 eV above the ground state with large transition moments of... 

If we suppose that these Rydberg states have non-negligible lifetimes against autoionization, as could occur via dispersion of the potential energy of the molecule into various vibrational modes, then these states would be very sensitive to electric fields in the measuring apparatus. It is suggested here that this is the reason for the large discrepancies between cross sections measured in the various beam experiments. 

The ZEKE-PFI practitioner relies on the existence of a narrow band of long-lived, high-n Rydberg states ( ZEKE states )15 lying just below each true cation threshold. If the shift of this band of states relative to the true threshold is essentially constant, then spectroscopic information extracted from differences in band frequencies will faithfully reflect the true cation energy levels. This assumption seems to hold to an accuracy of 1 cm-1 or better in the many molecules studied, as judged... 

Stebbings, R. F. Dunning, F. B. (Eds.) Rydberg States of Atoms and Molecules Cambridge University New York, 1983. 

The results for the A state show that a different mechanism is operative. A series of femtosecond pump-probe experiments were performed at wavelengths corresponding to the Rydberg states A (v = 0,1,2) of ammonia molecules.64-66,68,69 The wavelengths used to access these vibrational levels were 214 nm, 211 nm, and 208 nm for the pump laser and 321 nm, 316.5 nm, and 312 nm for the probe laser, respectively. 

Below the photoionisation threshold a core electron in a free molecule can be excited into empty anti-bonding molecular orbitals (m.o. s) as well as into Rydberg states. These transitions are observable as sharp features directly below the corresponding absorption edge (carbon K, oxygen K etc.). Above the... 

Whereas widely extended orbitals occur in the Rydberg states of gaseous molecules, and in many solids, they do not usually occur in solution, and the very large a values just discussed would not have so much chemical significance. 

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