Photoelectron circular dichroism (PECD) is a highly sensitive enantiospecific spectroscopy for studying chiral molecules in the gas phase using either single-photon ionization or multiphoton ionization. In the short pulse limit investigated with femtosecond lasers, resonance-enhanced multiphoton ionization (REMPI) is rather instantaneous and typically occurs simultaneously via more than one vibrational or electronic intermediate state due to limited frequency resolution. In contrast, vibrational resolution in the REMPI spectrum can be achieved using nanosecond lasers. In this work, we follow the high-resolution approach using a tunable narrow-band nanosecond laser to measure REMPI-PECD through distinct vibrational levels in the intermediate 3s and 3p Rydberg states of fenchone. We observe the PECD to be essentially independent of the vibrational level. This behaviour of the chiral sensitivity may pave the way for enantiomer specific molecular identification in multi-component mixtures: one can specifically excite a sharp, vibrationally resolved transition of a distinct molecule to distinguish different chiral species in mixtures.

We report the production of highly spin-polarized Deuterium atoms via photodissociation of deuterium iodide at 270 nm. The velocity distribution of both the deuterium and iodine photodissociation products is performed via velocity mapping slice-imaging. Additionally, the angular momentum polarization of the iodine products is studied using polarization-sensitive ionization schemes. The results are consistent with excitation of the A 1 Π1 state followed by adiabatic dissociation. The process produces ∼100% electronically polarized deuterium atoms at the time of dissociation, which is then converted to ∼ 60% nuclear D polarization after ∼ 1.6 ns. These production times for hyperpolarized deuterium allow collision-limited densities of ∼ 10 18 cm −3 , which is ∼ 10 6 times higher than conventional (Stern-Gerlach separation) methods. We discuss how such high-density hyperpolarized deuterium atoms can be combined with laser fusion to measure polarized D-D fusion cross sections.PACS numbers: 33.80. Gj, 32.10.Fn Controlling the nuclear spin polarization in fusion reactions offers important advantages, such as larger reaction cross sections, control over the emission direction of products, and in some cases eliminating hazardous neutron emission [1,2]. In the case of the five-nucleon reactions D + T → n + 4 He and D + 3 He → p + 4 He, it is well known that the reaction cross section increases by ∼50% when the fused nuclei have oriented nuclear spins [3,4].For the 4-nucleon D+D reaction, over the important energy range of 10-100 keV, the situation is unclear, since several predictions range from enhancement of the reaction, suppression of the reaction, or almost no effect at all [5][6][7][8][9][10]. The technical challenges of measuring fusion polarization dynamics limits the number of experiments which pursue this direction to two facility-scale experiments [11]. These experiments achieve nuclear spin polarization by magnetically separating the nuclear spin states via the Stern-Gerlach effect in molecular beams, a process however which limits the achievable production rates to ∼ 10 16 atoms s −1 [2], and the projected D-D fusion reaction rate to as low as ∼0.01 neutrons s −1 [12]. Polarized solid deuterium targets can be produced where the densities can reach as high as 2.5 × 10 19 spins/cm 3 , albeit in much lower polarization close to 10% [13]. Another approach for the production of polarized sold fuel involves accumulating the hyperpolarized deuterium in specially coated storage cells [11].Laser photodissociation of hydrogen halides has been shown to produce highly polarized H atoms [14][15][16][17]. The photodissociation process initially polarizes the electron spin up to 100% (for photofragment velocities parallel to the propagation direction of the circularly-polarized dissociation laser) [18]; due to the hyperfine interaction, the polarization oscillates back and forth between the electronic and the nuclear spin on the ∼1-ns timescale. By terminating this polarization exchange appropriately, for example by ioni...

Multiphoto-fragmentation (i.e. photodissociation and photoionization) processes for CH3I determined by slice imaging and mass resolved multiphoton ionization (MR-MPI).

The multiphoton dynamics of CH3Br were probed by Mass Resolved MultiPhoton Ionization (MR-MPI), Slice Imaging and Photoelectron Imaging in the two-photon excitation region of 66 000 to 80 000 cm-1. Slice images of the CH3+ and Br+ photoproducts of ten two-photon resonant transitions to np and nd Rydberg states of the parent molecule were recorded. CH3+ ions dominate the mass spectra. Kinetic energy release spectra (KERs) were derived from slice and photoelectron images and anisotropy parameters were extracted from the angular distributions of the ions to identify the processes and the dynamics involved. At all wavelengths we observe three-photon excitations, via the two-photon resonant transitions to molecular Rydberg states, forming metastable, superexcited (CH3Br#) states which dissociate to form CH3 Rydberg states (CH3**) along with Br/Br*. A correlation between the parent Rydberg states excited and CH3** formed is evident. For the three highest excitation energies used, the CH3Br# metastable states also generate high kinetic energy fragments of CH3(X) and Br/Br*. In addition for two out of these three wavelengths we also measure one-photon photolysis of CH3Br in the A band forming CH3(X) in various vibrational modes and bromine atoms in the ground (Br) and spin-orbit excited (Br*) states.