Measurement of Photoionization Cross-Section for the Excited States of Atoms: A Review

Photoionization cross sections measurements of the excited states of lutetium and ytterbium in the near threshold region

In this work, the threshold photoionization cross sections from the excited states of lutetium and ytterbium atoms were investigated by the laser pump-probe scheme under the condition of saturated resonant excitation. We obtained the resonance enhanced multiphoton ionization spectra of the lutetium and ytterbium atoms of the lanthanide metals in the range of 307.50-312.50 nm and 265.00-269.00 nm, respectively; the photoionization cross sections of the 5d6s(1D)6p(2D05/2) and 5d6s(3D)6p(2P01/2) states of lutetium and the 4f13(2F0)5d6s2(J = 1) states of ytterbium above threshold regions (0.4-1.6 eV) were measured, and measured values ranged from 2.3 ± 0.2 to 17.7 ± 1.5 Mb.

Valence-shell ionization of acetyl cyanide: simulation of the photoelectron and infra-red spectra

The vibrational envelopes of the first and second lines of the acetyl cyanide valence photoelectron spectrum [Katsumata et al., J. Electron Spectrosc. Relat. Phenom., 2000, 49, 113] in the gas phase have been simulated considering the Taylor expansion of the dipole moment from zero up to the second order as well as the changes of geometries/frequencies/normal modes between the initial neutral electronic ground state and the final (15a'^(-1), 3a''^(-1)) cationic states. It is shown that the vibrational profile of the first band (A') extending over 3500 cm^-1 with a vibrational spacing of 500 cm^-1 is not due solely to the overtones (v = 0 → v' = 1, 2, 3,…) of the C-CO bending mode as previously suggested but results from a collection of (v = 0 → v' = 1) transitions with frequencies multiple of 500 cm^-1 associated with the CO stretching at 1550 cm^-1, C-C stretching at 1045 cm^-1 and C-CO, C-CN bending modes at 370/500 cm^-1 completed by combination bands. Our calculations also reveal that the structureless and asymmetric shape of the second band (A'') is due to the activation of the torsion mode at low-frequency (ω ≈ 150 cm^-1) induced by the rotation (60 degrees) of the methyl group blurring the main vibrational progression (ω ≈ 1115 cm^-1) corresponding to the cooperative motions of the methyl CH bending and C-CO bending/CO stretching. Infra-red spectra of the fundamental and both the 15a'^(-1) and 3a''^(-1) cationic states were finally simulated. In contrast to the photoemission spectra, the infrared intensity of the CO stretching motion is very weak. The spectra are mainly dominated by the v = 0 → v = 1 transition of the CN stretching and the CH symmetric bending/stretching modes, providing complementary information between photoemission and infra-red spectroscopies to capture the nature of the cationic states in acetyl-cyanide.