Towards molecular frame photoelectron angular distributions in polyatomic molecules from lab frame coherent rotational wavepacket evolution

Abstract

A theory and method for a matrix-based reconstruction of molecular frame (MF) photoelectron angular distributions (MFPADs) from laboratory frame (LF) measurements (LFPADs) is developed and basic applications are explored. As with prior studies of MF reconstruction, the experimental side of this protocol is based upon time-resolved LF measurements in which a rotational wavepacket is prepared and probed as a function of time via photoionization, followed by a numerical reconstruction routine. In contrast to other methodologies, the protocol presented here does not require determination of the photoionization matrix elements, and consequently takes the relatively simple numerical form of a matrix equation. Significantly, this simplicity allows the successful reconstruction of MFPADs for nonlinear polyatomic molecules with D nh point group symmetry. We numerically demonstrate this scheme for two realistic molecular photoionization cases: N 2 and C 2 H 4 . This new technique is expected to be generally applicable to a broad range of MF reconstruction problems involving photoionization of polyatomic molecules.

Trends in angle-resolved molecular photoelectron spectroscopy

“…The reconstruction of MFPADs from TRPADs in polyatomic has been further theoretically analyzed. 394 The key observation is that both LFPADs and MFPADs depend linearly from the dipole products (see formalism), and once the C LM KQ have been extracted in LF one can retrieve the corresponding coefficients in MF, and express the full MFPAD through them, bypassing the determination of the individual dipole matrix elements, by solving systems of linear equations (with generalized inverses in case of singularities) instead of quadratic regressions. This was demonstrated for N 2 and C 2 H 4 , making explicit use of molecular symmetry.…”

“…The reconstruction of MFPADs from TRPADs in polyatomic has been further theoretically analyzed. 394 The key observation is that both LFPADs and MFPADs depend linearly from the dipole products d ðÀÞ Elmg d…”

“…This was demonstrated for N 2 and C 2 H 4 , making explicit use of molecular symmetry. 394 Momentum analysis of LFPAD anisotropies relying on ultrafast time-energy-angle resolved observables, when an electron wave-packet launched by a pump pulse is probed by valence ionization, was recently proposed as a new method to access molecular frame electronic coherences, as demonstrated for dissociation of excited states of the NH 3 molecule. 1,395 Inner-shell ionization of aligned molecules: Femtosecond photoelectron diffraction…”

Vibrationally resolved photoelectron angular distributions of ammonia

“…In one way or another, MFPADs have been determined for a large number of molecular systems [22][23][24][25][26][27][28][29][30][31] and, in some cases, they have been successfully used to get structural information. [23][24][25][32][33][34] For example, polarization-averaged MFPADs resulting from K-shell ionization of the CH 4 molecule 24,25 show that the electrons are mainly ejected along the bond directions, thus providing a direct imaging of the molecular geometry. The same has been predicted to occur in K-shell ionization of other molecules.…”

Discrimination of Excited States of Acetylacetone through Theoretical Molecular-Frame Photoelectron Angular Distributions

“…Due to this renewed interest, measurements and analysis of MFPADs contributed to an unprecedented degree of detailed information about molecular photoionization processes [ 10 , 11 ], electron–electron correlation [ 12 ], selection rules and localization of charge and core holes [ 13 , 14 ]. Among the applications of the fully differential photoelectron angular distribution measurements in the molecular frame, it was recently demonstrated that MFPADs are sensitive probes of the molecular bond length [ 15 ] and molecular structure [ 16 ].…”