Direct Measurement of the Angular Dependence of the Single-Photon Ionization of Aligned N2 and CO2

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2008-10, Vol.112 (39), p.9382-9386
• Main Authors: Thomann, Isabell, Lock, Robynne, Sharma, Vandana, Gagnon, Etienne, Pratt, Stephen T, Kapteyn, Henry C, Murnane, Margaret M, Li, Wen
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp8023414

By combining a state-of-the-art high-harmonic ultrafast soft X-ray source with field-free dynamic alignment, we map the angular dependence of molecular photoionization yields for the first time for a nondissociative molecule. The observed modulation in ion yield as a function of molecular alignment is attributed to the molecular frame transition dipole moment of single-photon ionization to the X, A and B states of N2 + and CO2 +. Our data show that the transition dipoles for single-photon ionization of N2 and CO2 at 43 eV have larger perpendicular components than parallel ones. A direct comparison with published theoretical partial wave ionization cross-sections confirms these experimental observations, which are the first results to allow such comparison with theory for bound cation states. The results provide the first step toward a novel method for measuring molecular frame transition dipole matrix elements.