Reactions of translationally excited and thermal fluorine atoms with CH4 and CD4 molecules in solid argon

Abstract

Solid state reactions of fluorine with methane have been studied by ultraviolet laser photolysis of dilute mixtures of the two reagents in solid argon at 13–30 K. Using a combination of EPR and FTIR spectroscopies, three distinct mechanisms of product formation have been identified. At temperatures below 18 K, product formation is dominated by direct photolysis of F2–CH4 heterodimers, resulting in formation of closed-shell complexes HF–CH3F. A small fraction of reaction intermediate, a nonplanar methyl radical trapped in the reaction cage with HF and F, is also formed. This intermediate decays to product on a time scale of 103 s at 13 K after the photolysis period. Above 20 K, photogenerated F atoms undergo thermally activated diffusion in argon, and they react with isolated CH4 molecules to form CH3–HF complexes. The rate constant for this process is ∼10−25 cm3 s−1 at 20 K, and exhibits an activation energy of 1.7 kcal/mol. A third reaction channel involves reaction of F with CH4 to generate isolated planar methyl radicals by escape of the HF product from the reactive site. This channel has been observed for reactions of translationally excited F atoms (below 20 K) and thermally diffusing F atoms (during post-photolysis reactions above 20 K).

Lithium impurity recombination in solid para-hydrogen: A path integral quantum transition state theory study

“…On the other hand, the recombination of molecular species in rare gas solids has been the subject of many experimental studies. [50][51][52][53] While most of these are qualitative, a recent work 53 provides an estimate of the intrinsic decay rate. In this experiment, CH 3 , HF, and F were generated within the reactive region of an argon matrix by photolysis, and the unimolecular recombination rate was measured to be kϭ1.5ϫ10 Ϫ3 s Ϫ1 at 13 K. This number is comparable to the reaction rate estimated in this paper.…”

Peculiarities of EPR spectra of methyl radicals in quench-condensed krypton films

“…This is closely related to the rotational motion of the CH 3 radical in such matrices as frozen gases which averages out the hyperfine components, A xx and A yy , yielding a spectrum of axial symmetry with the perpendicu- It is quite reasonable to attribute the difference in the DA signs for the free and trapped molecules to a different effect a matrix has on A^and A || parameters. The nonzero Dg is, probably, a fingerprint of the nonplanar structure of the trapped methyl radical [6]. It has been shown earlier [4] that DA < 0 for both Ar and Kr matrices while Dg is negative for Ar and positive for Kr.…”

“…The nonzero Dg is, probably, a fingerprint of the nonplanar structure of the trapped methyl radical [6]. It has been shown earlier [4] that DA < 0 for both Ar and Kr matrices while Dg is negative for Ar and positive for Kr.…”

Low-temperature tunneling of CH3 quantum rotor in van der Waals solids

“…. Notice the trend of decreasing rotational correlation time with increasing atomic radius of the host of CH 3 in molecular hydrogen H 2 and solid noble gases Ne, Ar, Kr[12,27], while the later was observed in solid gases consisting of the linear CO, N 2 O, CO 2 molecules…”