Transfer of a proton between H2 and O2

Area of Science:

• Astrochemistry
• Physical Chemistry
• Spectroscopy

Background:

• The similar proton affinities of hydrogen and oxygen suggest a near thermoneutral proton transfer reaction: H(3)(+) + O(2) <--> O(2)H(+) + H(2).
• This reaction is hypothesized to be a primary mechanism for binding interstellar oxygen into the oxonium ion (O(2)H(+)).

Purpose of the Study:

• To investigate the kinetics of the H(3)(+) + O(2) proton transfer reaction across a wide temperature range.
• To determine the activation energy for the forward reaction and its implications for interstellar environments.
• To explore spectroscopic signatures of O(2)H(+) and probe the energy level populations of H(3)(+).

Main Methods:

• Utilized a low-temperature 22-pole ion trap to study the reaction from 280 K down to approximately 40 K.
• Analyzed the temperature dependence of the rate coefficient to determine the activation energy.
• Employed laser-induced reactions to search for O(2)H(+) spectroscopic signatures and probe H(3)(+) populations.

Main Results:

• The forward reaction rate coefficient exhibits Arrhenius behavior with an activation energy of E(A)/k = 113 K.
• This activation energy indicates the reaction is only significant in higher-temperature molecular clouds.
• Preliminary infrared spectroscopic searches for O(2)H(+) were unsuccessful; however, the forward reaction effectively probed H(3)(+) ortho and para level populations.

Conclusions:

• The proton transfer reaction H(3)(+) + O(2) requires a notable activation energy, limiting its role in cold interstellar regions.
• The study provides crucial kinetic data for astrochemical models concerning oxygen incorporation into O(2)H(+).
• Further spectroscopic investigations are needed to detect O(2)H(+) directly, while H(3)(+) population measurements offer insights into interstellar conditions.