Laser detection of spin-polarized hydrogen from HCl and HBr photodissociation: Comparison of H- and halogen-atom polarizations

Abstract

Thermal HCl and HBr molecules were photodissociated using circularly polarized 193 nm light, and the speed-dependent spin polarization of the H-atom photofragments was measured using polarized fluorescence at 121.6 nm. Both polarization components, described by the a(0)(1)(perpendicular) and Re[a(1)(1)(parallel, perpendicular)] parameters which arise from incoherent and coherent dissociation mechanisms, are measured. The values of the a(0)(1)(perpendicular) parameter, for both HCl and HBr photodissociation, are within experimental error of the predictions of both ab initio calculations and of previous measurements of the polarization of the halide cofragments. The experimental and ab initio theoretical values of the Re[a(1)(1)(parallel, perpendicular)] parameter show some disagreement, suggesting that further theoretical investigations are required. Overall, good agreement occurs despite the fact that the current experiments photodissociate molecules at 295 K, whereas previous measurements were conducted at rotational temperatures of about 15 K.

Imaging detection of spin-polarized hydrogen atoms

“…This result is plotted in Figure 4 along with theoretical values obtained as described above. We also show the value from Rakitzis and coworkers [6] obtained at 193 nm, after converting to the lab frame using the expression a (1) 0 (⊥) = 6˛1/(2 − ˇ) [12]. The measured polarization is somewhat lower than the predicted value, just outside of the 2 uncertainty.…”

“…The first such determinations were inferences based upon measurements of the cofragment angular momentum polarization for diatomic systems [4,5]. Subsequently, spin-polarized hydrogen (SPH) was directly measured under bulb conditions monitoring polarized VUV fluorescence, albeit with velocity resolution limited by a vacuum ultraviolet Doppler probe [6]. Very recently, we developed a direct probe of the velocity-dependent H atom spin polarization by adapting the H atom Rydberg time-of-flight technique [7,8].…”

“…The red circle was obtained in this work. The blue square was obtained by Sofikitis et al[6]. Error bars are 2 .…”

Highly Nuclear-Spin-Polarized Deuterium Atoms from the UV Photodissociation of Deuterium Iodide

“…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.…”

“…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.…”