Rotational Cooling Effect on the Rate Constant in the CH₃F + Ca⁺ Reaction at Low Collision Energies

Abstract

The rotational cooling effect on the reaction rate constant of the gas-phase ion–polar-molecule reaction CH3F + Ca+ → CH3 + CaF+ was experimentally studied at low collision energies. Fluoromethane molecules showed higher reactivity as the rotational temperature decreased. The experimental rate constants were compared with the capture rate constants which were obtained by the Perturbed Rotational State (PRS) theory assuming the rotational level distribution corresponding to the experimental conditions. The PRS result shows a strong dependence of the capture rate constants on the rotational level distribution in accordance with the experimental findings. However, the PRS capture rate constants deviate from the measurement values as the average collision energy increases especially when the fluoromethane molecules are rotationally cooled far below room temperature. The present paper suggests that the rotational state distribution significantly affects the rate constants of ion–polar-molecule reactions and is one of the important issues to be considered in the study of molecular synthesis in the interstellar medium, where the thermal equilibrium is not necessarily established.

10 Years of the ACS PHYS Astrochemistry Subdivision

“…However, this is hardly the only novel result. In this virtual special issue, N 2 O is reacted with C­( 3 P), producing rate coefficients for such chemical processes, and a similar study on fluoromethane and calcium atomic cations is also reported . Additionally, the deuterated ethynyl radical is reacted with propylene producing a wealth of hydrocarbons, NO + the propargyl radical generates branching ratios for eight common astrochemical products, furan + H 2 reactions generate various c -C 4 H x O ( x = 4–8) species, myriad nitrous oxides are synthesized in H 2 O–N 2 O/N 2 ice mixtures, , dinitriles are shown to be produced from gas-phase reactions of cyano radicals and cyanoethane, and porous amorphous solid water appears to catalyze interstellar organic chemistry .…”

“…In this virtual special issue, N 2 O is reacted with C( 3 P), producing rate coefficients for such chemical processes, 21 and a similar study on fluoromethane and calcium atomic cations is also reported. 22 Additionally, the deuterated ethynyl radical is reacted with propylene producing a wealth of hydrocarbons, 23 NO + the propargyl radical generates branching ratios for eight common astrochemical products, 24 furan + H 2 reactions generate various c-C 4 H x O (x = 4−8) species, 25 myriad nitrous oxides are synthesized in H 2 O−N 2 O/N 2 ice mixtures, 26,27 dinitriles are shown to be produced from gas-phase reactions of cyano radicals and cyanoethane, 28 and porous amorphous solid water appears to catalyze interstellar organic chemistry. 29 From theory, the earliest molecule in the universe (HeH + ) is most efficiently rotationally excited by collisions with H 2 , 30 H 2 CCS and HCCSH are likely not detected since they are destroyed through barrierless reactions with atomic hydrogen, 31 and MgNC reacts with water clusters to produce the known HMgNC molecule along with other Mg-containing species.…”

Spatial and Temporal Detection of Ions Ejected from Coulomb Crystals

“…The use of trapping and laser cooling methods to produce ensembles of translationally cold ions is an area of active research interest. Much of this interest is inspired by the diverse range of applications for cold, confined ionsincluding their use as qubits, , in the determination of fundamental constants, , for precision measurements, − and for the study of chemical reaction dynamics and kinetics. − As many ionic species of interest cannot be easily or efficiently laser-cooled, Coulomb crystals have emerged as a useful tool for the study of processes involving sympathetically cooled trapped ions.…”