Generation of cold polyatomic cations by cascade reactive two-body ion-atom collisions

Abstract

Polyatomic cations ${}^{87}$Rb${}_M^{+}$ ($M$ = 2, 3,$\dots$) have been produced by cascade two-body ion-atom reactive collisions in the two-step CW-laser photoionization of laser-cooled ${}^{87}$Rb atoms and accumulated in the ion trap. Using resonant-excitation mass spectrometry and resonant excitation-assisted time-of-flight mass spectrometry, we directly observed and distinguished the charged reaction products. We experimentally verified the cascade generation and cascade dissociation of ${}^{87}$Rb${}_M^{+}$. The populations of ${}^{87}$Rb${}_M^{+}$ are quantitatively investigated by solving the rate equations. The ${}^{87}$Rb${}^{+}$-${}^{87}$Rb reaction rate coefficient was derived as 9.10$\times 10^{-11}$ cm${}^3$/s accordingly. The methods developed here for assembling and detecting homonuclear polyatomic cations can be applied to any experiment in ion-atom hybrid traps. The present study lays the foundation for exploring atomically precise metal clusters and physics from few- to many-body perspective.

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