Direct measurement of the angular dependence of the single-photon ionization of aligned N2 and CO2.
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.
Thomann
Isabell
I
JILA and Department of Physics, University of Colorado and NIST, Boulder, Colorado 80309, USA.
Lock
Robynne
R
Sharma
Vandana
V
Gagnon
Etienne
E
Pratt
Stephen T
ST
Kapteyn
Henry C
HC
Murnane
Margaret M
MM
Li
Wen
W