The role of H atoms in astrochemistry

Luca, Gerlich, ....

Introduction

Astronomer’s periodic table, Early universe, hot and cold environments

spectroscopic characterization, Lyman alpha, 21 cm

Interesting questions: H₂ formation: gas phase or grains?

basic reaction dynamics: H + H₂

chemistry: bond activation by H atoms

Not included are: Neutral - H collisions, Surface - H collisions

Brief survey of theoretical treatments

Potential surfaces

Exchange symmetry

Classical trajectories calculation

Small barriers - low temperatures

Tunneling “Quasiclassical”

Statistical theories

Experimental

Sources of atomic hydrogen target

Thermal cracking, plasma discharge,

Cooling of H atoms

Hexapole magnetic fields

TOF analysis

Trapping H atoms, (Bose-Einstein condensate)

Typical experimental setups for ion - H collisions

ICR

SIFT, VT-SIFT, SIFDT

22PT

merged beam (H^‑ H)

Selected reaction systems

Charge transfer reactions

H⁺ + D ↔ D⁺ + H

X⁺ + H / D, XY⁺ + H

• Hydrogen abstraction reactions

Hydrocarbons, saturations with H2, activation with H

CH⁺ + H / D , NH⁺ + H / D

CH₄⁺ + H, CH₅⁺ + H / D

PAH⁺ + H

Thermoneutral processes and small barriers in ion molecule reactions

CH₄⁺ + H₂ ↔ CH₅⁺ + H

C₂H₃⁺ + H , C₃H₂⁺ + H

Association reactions

Radiative association with H atoms

CH₃⁺ + H -> k = ?

Atoms sticking

Atoms scrambling and nuclear spin relaxation

H₂⁺ + H ↔ H₂⁺ + H

H₃⁺ + H, D₃⁺ + H

Deuteration with D atoms

DCO⁺ + H ↔ HCO⁺ + D

DN₂⁺ + H ↔ HN₂⁺ + D

CH₅⁺ + D

Negative Ion chemistry

C₇H ^‑, H ^‑