Pinpointing the role of geometric phase: During chemical reactions, electrons usually rearrange more quickly than nuclei. Thus, theorists often adopt an adiabatic framework that considers vibrational and rotational dynamics within single electronic states. Near the regime where two electronic states intersect, the dynamics get more complicated, and a geometric phase factor is introduced to maintain the simplifying power of the adiabatic treatment. Yuan et al. conducted precise experimental measurements that validate this approach. They studied the elementary H + HD reaction at energies just above the intersection of electronic states and observed angular oscillations in the product-state cross sections that are well reproduced by simulations that include the geometric phase. Science , this issue p. 1289

In order determine whether formate is a reaction intermediate of the direct pathway for formic acid oxidation at a Pt electrode, formic acid (HCOOH) oxidation at a Pt(111) electrode has been studied by normal and fast scan voltammetry in 0.1 M HClO₄ solutions with different HCOOH concentrations. The relationship between the HCOOH oxidation current density (j_ox) and formate coverage (θ_formate) is quantitatively analyzed. The kinetic simulation reveals that the previously proposed formate pathway, with decomposition of the bridge-bonded formate (HCOO_B) as a rate determining step (rds), cannot be the main pathway responsible for the majority of the current for HCOOH oxidation. Instead, a kinetic model based on a mechanism with formic acid adsorption , along with simultaneous C–H bond activation as the rds for the direct pathway, explains the measured data well. It was found for the relatively slow rate of formic acid oxidation, that adsorption–desorption of the formate is faster, which competes for the surface sites for formic acid oxidation.

Intriguing dynamics pattern in F + HD: Despite decades of studies, the role of relativistic spin-orbit interactions in the dynamics of chemical reactions remains an intriguing topic. Using a high-resolution velocity map imaging crossed beams technique, Chen et al. observed an interesting pattern in the differential cross sections in the F + HD → HF + D reaction near the partial wave resonances (see the Perspective by Rakitzis). Further theoretical analysis showed that this pattern originates from quantum interference between spin-orbit split partial wave resonances with different total parities. The effect of the fine structure of the partial waves observed for this long known yet not completely explored three-atom system represents one more remarkable demonstration of the truly quantum nature of chemical reaction dynamics. Science , this issue p. 936 ; see also p. 886

We report the observation of a $\pi$-type dipole-bound state ($\pi$-DBS) in cryogenically cooled deprotonated 9-anthrol molecular anions ($9{\mathrm{AT}}^{-}$) by resonant two-photon photoelectron imaging. A DBS is observed $191{\mathrm{cm}}^{-1}$ (0.0237 eV) below the detachment threshold, and the existence of the $\pi$-DBS is revealed by a distinct ($s+d$)-wave photoelectron angular distribution. The $\pi$-DBS is stabilized by the large anisotropic in-plane polarizability of 9AT. The population of the dipole-forbidden $\pi$-DBS is proposed to be via a nonadiabatic coupling with the dipole-allowed $\sigma$-type DBS mediated by molecular rotations.