Dissociative recombination of CH4(+).

Area of Science:

• Astrochemistry
• Chemical Physics
• Plasma Physics

Background:

• CH4(+) is a key molecular ion in various astronomical environments, including interstellar clouds and planetary atmospheres.
• Dissociative recombination (DR) is a primary destruction pathway for CH4(+), but its rate has been uncertain.
• Accurate DR rates are essential for modeling the chemical evolution of these regions.

Purpose of the Study:

• To experimentally determine the absolute cross-sections and rate constants for the dissociative recombination of CH4(+).
• To investigate the product branching fractions of the DR process at low collision energies.
• To improve the accuracy of astrochemical models by providing reliable data for CH4(+) destruction.

Main Methods:

• Absolute measurements of CH4(+) dissociative recombination were performed using the CRYRING heavy-ion storage ring.
• Collision-energy dependent cross-sections were measured.
• Branching fractions of DR products were determined at low collision energies.

Main Results:

• A thermal rate constant was inferred: k(Te) = 1.71(±0.02) × 10(–6)(Te/300)(−0.66(±0.02)) cm3 s(–1) for 10 ≤ Te ≤ 1000 K.
• Branching fractions revealed that 80% of DR collisions result in the breaking of two or more C–H bonds.
• Specific product channels include CH3 + H, CH2 + 2H, CH2 + H2, CH + H2 + H, and CH + 2H2.

Conclusions:

• The study provides precise measurements of the CH4(+) DR rate constant, reducing uncertainty in astrochemical models.
• The product distribution indicates significant fragmentation, with multiple C–H bond dissociations being dominant.
• These results contribute to a better understanding of ion chemistry in diffuse clouds, dense clouds, cometary comae, and planetary ionospheres.