Contrast between the mechanisms for dissociative electron attachment to CH3SCN and CH3NCS

Abstract

The kinetics of thermal electron attachment to methyl thiocyanate (CHSCN), methyl isothiocyanate (CHNCS), and ethyl thiocyanate (CHSCN) were measured using flowing afterglow-Langmuir probe apparatuses at temperatures between 300 and 1000 K. CHSCN and CHSCN undergo inefficient dissociative attachment to yield primarily SCN at 300 K (k = 2 × 10 cm s), with increasing efficiency as temperature increases. The increase is well described by activation energies of 0.17 eV (CHSCN) and 0.14 eV (CHSCN). CN product is formed at <1% branching at 300 K, increasing to ∼30% branching at 1000 K. Attachment to CHNCS yields exclusively SCN ionic product but at a rate at 300 K that is below our detection threshold (k < 10 cm s). The rate coefficient increases rapidly with increasing temperature (k = 6 × 10 cm s at 600 K), in a manner well described by an activation energy of 0.51 eV. Calculations at the B3LYP/def2-TZVPPD level suggest that attachment to CHSCN proceeds through a dissociative state of CHSCN, while attachment to CHNCS initially forms a weakly bound transient anion CHNCS that isomerizes over an energetic barrier to yield SCN. Kinetic modeling of the two systems is performed in an attempt to identify a kinetic signature differentiating the two mechanisms. The kinetic modeling reproduces the CHNCS data only if dissociation through the transient anion is considered.

Nitrogen Triflorida (NF3) : Termodinamika dan Transpor Elektron NF3

“…Percobaan telah menunjukkan bahwa ion negatif F− adalah produk dominan dari keterikatan disosiatif elektron (186)(187)(188)(189)(190)(191) . Penampang untuk proses ini adalah antara dua hingga empat lipat lebih besar dari yang untuk penciptaan F−2 dan NF−2 ion Kami menggunakan penampang eksitasi getaran dari Dyatko dan Napartovich, eksitasi disosiatif (192)(193)(194) penampang Rescigno , dan ionisasi eksperimental penampang dari Tarnovsky.…”