Optical Control of Reactions between Water and Laser-Cooled Be⁺ Ions

Area of Science:

• Chemical Physics
• Atomic and Molecular Physics
• Physical Chemistry

Background:

• Understanding ion-molecule reactions is crucial for various fields, including atmospheric chemistry and plasma physics.
• Beryllium ion (Be+) reactions with water are not well-characterized, particularly concerning the influence of electronic states on reactivity.

Purpose of the Study:

• To experimentally measure reaction rate coefficients for Be+ with H2O in both ground and excited electronic states.
• To investigate the reaction dynamics and identify key factors influencing reactivity, such as potential energy surfaces and electronic state effects.

Main Methods:

• Utilizing a combined ion trap and time-of-flight mass spectrometry system for precise measurement of individual reaction rates.
• Performing zero-point-corrected quasi-classical trajectory calculations on an accurate potential energy surface.
• Employing laser excitation to probe reactions from the Be+ excited state.

Main Results:

• The rate coefficient for Be+(2S1/2) + H2O → BeOH+ + H is reported for the first time, found to be ~2x lower than capture model predictions.
• Calculations indicate the ground state reaction is capture-dominated but hindered by a submerged barrier.
• Excited state Be+(2P3/2) reactions exhibit new channels (BeOH+ + H and H2O+ + Be) with nonadiabatic dynamics.

Conclusions:

• The reactivity of Be+ with water is significantly influenced by electronic state and subtle features of the potential energy surface.
• Submerged barriers can reduce ion-molecule reaction rates below predictions from simple capture models.
• Laser-induced electronic excitation provides a pathway to control and study nonadiabatic reaction dynamics.