Ion-Molecule Reactions below 1 K: Strong Enhancement of the Reaction Rate of the Ion-Dipole Reaction He+ + CH3F
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2020-12-31
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Journal Article
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Abstract
The reaction between He+ and CH3F forming predominantly CH+2 and CHF+ has been studied at collision energies Ecoll between 0 and kB⋅10 K in a merged-beam apparatus. To avoid heating of the ions by stray electric fields, the reaction was observed within the orbit of a highly excited Rydberg electron. Supersonic beams of CH3F and He(n) Rydberg atoms with principal quantum number n=30 and 35 were merged and their relative velocity tuned using a Rydberg-Stark decelerator and deflector, allowing an energy resolution of 150 mK. A strong enhancement of the reaction rate was observed below Ecoll/kB=1 K. The experimental results are interpreted with an adiabatic capture model that accounts for the state-dependent orientation of the polar CH3F molecules by the Stark effect as they approach the He+ ion. The enhancement of the reaction rate at low collision energies is primarily attributed to para-CH3F molecules in the J=1, KM=1 high-field-seeking states, which represent about 8% of the population at the 6 K rotational temperature of the supersonic beam.
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published
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125 (26)
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263401
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American Physical Society
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03449 - Merkt, Frédéric / Merkt, Frédéric
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743121 - Cold Ion Chemistry - Experiments within a Rydberg Orbit (EC)
172620 - Precision measurements with cold molecules: Rydberg states, ions and photoionization (SNF)
172620 - Precision measurements with cold molecules: Rydberg states, ions and photoionization (SNF)