Dynamics of Rotationally Resolved Multiphoton Ionization Processes in Molecules

Author: Rudolph, Henrik

Year: 1989

Degree: Dissertation (Ph.D.)

Advisor: McKoy, Basil Vincent

Committee Members: Zewail, Ahmed H.; McKoy, Basil Vincent; Bercaw, John E.; Okumura, Mitchio

Option: Chemistry

DOI: 10.7907/981t-6997

Abstract

This dissertation presents the results of studies of several rotationally-resolved resonance enhanced multiphoton ionization (REMPI) processes in some simple molecular systems. The objective of these studies is to quantitatively identify the underlying dynamics of this highly state-specific process which utilizes the narrow bandwidth radiation of a laser to ionize a molecule by first preparing an excited state via multiphoton absorption and subsequently ionizing that state before it can decay. Coupled with high-resolution photoelectron spectroscopy, REMPI is clearly an important probe of molecular excited states and their photoioniza tion dynamics.

A key feature of our studies is that they are carried out using accurate Hartree-Fock orbitals to describe the photoelectron orbitals of the molecular ions. The use of such photoelectron orbitals is important in rotationally-resolved studies where the angular momentum coupling in the photoelectron orbital plays a significant role in the photoionization dynamics. In these studies the Hartree-Fock molecular molecular photoelectron orbitals are obtained by numerical solution of a Lippmann-Schwinger integral equation.

Studies reported here include investigations of (i) ionic rotational branching ratios and their energy dependence for REMPI via the A2Σ+(3sσ) and D2Σ+(3pσ)states of NO, (ii) the influence of angular momentum constraints on branching ratios at low photoelectron energies for REMPI via low-J levels of the resonant intermediate state, (iii) the strong dependence of photoelectron angular distributions on final ionic rotational state and on the alignment in REMPI of the A2Σ+ state of NO, (iv) vibrational state dependence of ionic rotational branching ratios arising from rapid orbital evolution in resonant states (E'2Σ+(3pσ) of CH), (v) the influence of rovibronic interactions on the rotational branching ratios seen in REMPI via the D2Σ+(3pσ) state of NO, and (vi) effects of laser intensity on the photoionization dynamics of REMPI.

Files