Electrically tuned Förster resonances in collisions of NH${}_3$ with Rydberg He atoms

Abstract

Effects of weak electric fields on resonant energy transfer between NH${}_3$ in the X ${}^1$A${}_1$ ground electronic state, and Rydberg He atoms in triplet states with principal quantum numbers $n=36$-$41$ have been studied in a crossed beam apparatus. For these values of $n$, electric-dipole transitions between the Rydberg states that evolve adiabatically to the $|ns⟩$ and $|np⟩$ states in zero electric field can be tuned into resonance with the ground-state inversion transitions in NH${}_3$ using electric fields, with energy transfer occurring via Förster resonance. In the experiments the Rydberg He atoms, traveling in pulsed supersonic beams, were prepared by resonant two-photon excitation from the metastable $1s2s{}^3{S}_1$ level and crossed an effusive beam of NH${}_3$ before being detected by state-selective pulsed-electric-field ionization. The resonant-energy-transfer process was identified by monitoring changes in the ionization signal from the $|ns⟩$ and $|np⟩$ Rydberg states for each value of $n$. The electric field dependence of the experimental data is in good agreement with the results of calculations in which the resonant dipole-dipole coupling between the collision partners was accounted for.

6 pages, 4 figures