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Updated: Jan 13, 2026

Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization

Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization

Published on: August 6, 2018

ヘリウムナノ液滴中の（NH₃-H₂O）⁺ラジカルカチオンの赤外分光法

Tom C Bernaards¹, Amandeep Singh¹, Zane Golpariani¹

¹Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.

The journal of physical chemistry letters

|January 9, 2026

Abstract:

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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ヘリウムナノ液滴ラジカルカチオンアンモニア水赤外分光法クラスター異性体

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