Direct observation of field-free alignment of asymmetric molecules in excited states

Abstract

The excited state dynamics of o-dichlorobenzene has been studied by femtosecond time-resolved photoelectron imaging. The lifetime of the first excited state S 1 of o-dichlorobenzene was determined to be 482 ± 10 ps. Fieldfree nonadiabatic alignment of the o-dichlorobenzene on the first excited state S 1 (with an asymmetry parameter k = 0.153) by a femtosecond laser pulse was observed via time-resolved photoelectron angular distributions. Rotational wave packet revivals on the S 1 state of the typical asymmetric molecule o-dichlorobenzene at 296 ps has been measured.

Imaging the breakdown of molecular-frame dynamics through rotational uncoupling

“…3(c) along with the typical Born-Oppenheimer signal for comparison. The measured time-dependent PAD shows no evidence of the half and full rotational revival periods near 4.3 and 8.7 ps, which are the expected signatures of coherent rotational wave packets in Born-Oppenheimer molecular systems [3,29]. Instead, the quantum beats in the angular distribution correspond to the small electronic splittings of the 4f manifold in the presence of the anisotropic core.…”

“…The result is a PAD which is entirely insensitive to the molecular frame motion. This is in contrast to the excitation of a low-lying valence electronic state, where the electron wave function follows the instantaneous orientation of the molecular frame and the time-dependent PAD exhibits large variation in the β parameters only near the quantum revivals of the rotational wave packet [3,29].…”

“…In the standard Born-Oppenheimer picture, electrons occupy orbitals that are fixed to the molecular frame and display the symmetries of the underlying molecular structure. Recent experiments in ultrafast and strong field physics have utilized aligned ensembles of molecules, allowing for molecular frame measurements of excited state dynamics [1][2][3][4] and XUV and tunnel ionization [5][6][7][8][9][10] that are sensitive to electron orbital geometry. This simple picture breaks down for non-penetrating Rydberg electrons, where the electron wave function has minimal overlap with the ion-core.…”

Ultrafast excited-state dynamics in a prototype of the peptide bond: Internal conversion of the isolated N,N-dimethylformamide

“…TRPEI experiments were performed by combining a femtosecond laser system with the velocity map imaging apparatus, which has been described in detail elsewhere [15,16].…”

Ultrafast Internal Conversion Dynamics of 2-Chloropyridine by Femtosecond Time-Resolved Photoelectron Imaging

“…The time-resolved photoelectron imaging setup employed in this study has been described in detail elsewhere. 22,23 Briefly, the molecular beam apparatus consists of a beam source and a main chamber, both of which are pumped by turbo-molecular pumps. The liquid sample (2-chloropyridine, 99.9% purity), 5% seeded in helium buffer gas at a background pressure of 2.02×10 -5 Pa, was expanded through a pulsed valve to generate a pulsed molecular beam.…”