_Publication history_ - Original document (Authorea), DOI: 10.22541/au.149030711.19068540. - arXiv 1702.00744 (Feb. 2017) - J. Chem. Phys. special issue “Developments and Applications of Velocity Mapped Imaging Techniques”, (March 2017), DOI: 10.1063/1.4978923 - Data and analysis scripts (OSF), DOI: 10.17605/OSF.IO/RRFK3. _See also_ - AIP Press Release: _The Inner Lives of Molecules_ (April 2017) - PImMS camera website - Vallance group website - Femtolab website
Time-resolved pump-probe measurements of Xe, pumped at 133 nm and probed at 266 nm, are presented. The pump pulse prepared a long-lived hyperfine wavepacket, in the Xe 5p⁵(²P1/2∘)6s ²[1/2]₁∘ manifold (E=77185 cm −1=9.57 eV). The wavepacket was monitored via single-photon ionization, and photoelectron images measured. The images provide angle- and time-resolved data which, when obtained over a large time-window (900 ps), constitute a precision quantum beat spectroscopy measurement of the hyperfine state splittings. Additionally, analysis of the full photoelectron image stack provides a quantum beat imaging modality, in which the Fourier components of the photoelectron images correlated with specific beat components can be obtained. This may also permit the extraction of isotope-resolved photoelectron images in the frequency domain, in cases where nuclear spins (hence beat components) can be uniquely assigned to specific isotopes (as herein), and also provides phase information. The information content of both raw, and inverted, image stacks is investigated, suggesting the utility of the Fourier analysis methodology in cases where images cannot be inverted.
INTRODUCTION Measurements in the molecular frame help elucidate the fundamental physics of molecules. The physics of molecules in turn inform the nature of interaction between a number of quantum particles, important for both the understanding of larger systems and that of fundamental quantum phenomena. Measurements made in the laboratory frame from randomly oriented molecules, or a thermal mixture of numerous angular momentum states, result in a loss of information due to incoherent averaging over the orientations, or equivalently, the rotational states. Methods to overcome this either coherently drive a large number of rotational states, or select the ground rotational state from an ensemble. Either scenerio results in spatially anisotropic distribution, with the former approaching the molecular frame as the distribution of rotational states broadens. This is the preferred method in ultrafast physics, since the time resolution allows for measurements at the moment of sharpest alignment. The latter method is typically applied for precision spectroscopic measurements. Recent advances in laser cooling of di- and tr-atomic linear molecules has enabled coherent selection of the ground rotational state, allowing for precise spectroscopic measurements of dissociative molecular states.