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Updated: Jan 13, 2026

Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization
Published on: August 6, 2018
Infrared Spectroscopy of (NH3-H2O)+ Radical Cations in Helium Nanodroplets
Tom C Bernaards1, Amandeep Singh1, Zane Golpariani1
1Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
None:
Radical cation clusters such as (NH3-H2O)+ remain elusive because in typical molecular beam experiments they rapidly react with molecules and neutral clusters to produce protonated clusters. Ionization of neutral NH3-H2O clusters in helium droplets enables isolation of the primary ionization products, a large fraction of which is found to be (NH3-H2O)+ cations. These cations were studied via laser infrared spectroscopy and their structures were determined based on comparison to results of previous quantum chemical calculations. The formation of the cations via the electron impact ionization of the corresponding neutral dimers yielded two distinct isomers, containing either an NH3+ or NH4+ ion core. We also found that the lowest energy isomer, H2NH+-OH2, could be selectively produced upon the reaction of preformed NH3+ embedded in helium droplets with H2O molecules added to the droplets downstream. This work shows that helium droplets can serve as a vehicle to study ion-molecule reactions between two well-defined reactants.
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