Pattern analysis of the impact‐parameter dependent trajectory for the H + H2 exchange reaction was performed at temperatures T = 3 and 300 K by employing the quasi‐classical trajectory calculation on a London‐Eyring‐Polanyi‐Sato surface. We find that (a) 0.66 fraction of reactive trajectories throughout b = 0.0 ~ 5.0 Å at T = 3 K, while only 0.33 at T = 300 K only for b = 0.0 ~ 1.5 Å and decreases soon to zero for b = 2.5 ~ 5.0 Å. (b) Ninety eight percent of the trajectories showed direct collision pattern at T = 300 K, while at T = 3 K, 72% for direct collision trajectories and 28% showed the intermediate H + H2 complex formation pattern. These results suggest that nonzero impact‐parameter trajectories play a role at T = 3 K to enhance reactivity due to long‐range attraction forces. Trajectory pattern analysis reveals a characteristic propensity rule between the amplitude of the time‐dependent interaction potential and the trajectory reactivity, thus we can judge if a trajectory is reactive or nonreactive. The analysis also proposes a roaming‐like libration motion at T = 3 K like in the interstellar clouds.

Gold nanoparticles (AuNPs) are used in many applications including in cancer therapy. One way to improve the quality of treatment is to design AuNPs to provide optimum adsorption to the radionuclides being employed. Therefore, we have to first understand the mechanism and quantify the strength of such adsorption process. This study looks at the adsorption characteristics of iodine and astatine on gold nanoparticles, specifically the (111) surface to learn more about adsorption of such heavy elements on Au surfaces. Both iodine and astatine are found to be able to bond with Au(111) via covalent bonding most stably on the face-centered cubic (fcc) site. We also found that the adsorption strength of iodine and astatine on gold are comparable, and that spin orbit coupling correction does not significantly affect the adsorption energies.

Astatine-211 (211At or simply At) used as an α particle emitter is currently gaining as treatment method for cancer cells. It must however be attached to a carrier to facilitate the treatment process. Gold nanoparticle is a good candidate that has been used in several tests. Knowing the physics behind the adsorption of astatine on gold nanoparticles would be advantageous in designing a more optimal method for such applications. We therefore performed density functional theory calculation on astatine adsorption on gold (111) surface to understand both the mechanism of astatine bonding with gold and the strength of the bonding. We found the mechanism of adsorption to be the hybridization between the 6p orbital of astatine and the 5d and 6s orbitals of the gold. We also found the adsorption strength of astatine on gold to be -1.43 eV at the fcc hollow site. Both results provide us with a good starting point towards our goal of designing an optimized gold nanoparticle for radiotherapy.