Infrared Spectrum of the Free Radical CF3 Isolated in Inert Matrices

Calculations of the active mode and energetic barrier to electron attachment to CF3 and comparison with kinetic modeling of experimental results

To provide a deeper understanding of the kinetics of electron attachment to CF₃, the six-dimensional potential energy surfaces of both CF₃ and CF₃^- were developed by fitting ∼3000 ab initio points per surface at the AE-CCSD(T)-F12a/AVTZ level using the permutation invariant polynomial-neural network (PIP-NN) approach. The fitted potential energy surfaces for CF₃ and CF₃^- had root mean square fitting errors relative to the ab initio calculations of 1.2 and 1.8 cm^-1, respectively. The main active mode for the crossing between the two potential energy surfaces was identified as the umbrella bending mode of CF₃ in C_3v symmetry. The lowest energy crossing point is located at R_CF = 1.306 Å and θ_FCF = 113.6° with the energy of 0.051 eV above the minimum of the CF₃ electronic surface. This value is only slightly larger than the experimental data 0.026 ± 0.01 eV determined by kinetic modeling of electron attachment to CF₃. The small discrepancy between the theoretical and experimentally measured values is analyzed.

Trifluoroselenoacetic acid, CF(3)C(O)SeH: preparation and properties

The hitherto unknown trifluoroselenoacetic acid was prepared through the reaction of trifluoroacetic acid with Woollins' reagent. The compound was fully characterized by mass spectrometry, (1)H, (19)F, (77)Se, and (13)C NMR, UV-visible, IR and Raman spectroscopy, and the boiling point at 46 °C was estimated from the vapor pressure curve. An IR matrix isolation study revealed the presence of two different syn-anti and anti-syn conformers. The IR spectra of the two stereoisomers have been assigned, aided by DFT, and ab initio calculations. The UV photolysis of Ar matrix isolated CF(3)C(O)SeH yielded CO, OCSe, CF(3)SeH, and CHF(3). Apart from CF(3)SeH, these products were also obtained by vacuum flash-pyrolysis (310 °C) of gaseous CF(3)C(O)SeH. Instead of CF(3)SeH, CF(2)Se, and HF were detected among the pyrolysis products. The different decomposition pathways of CF(3)C(O)SeH are discussed.

The Far-Infrared Laser Magnetic Resonance Spectrum of CH2F

Far-infrared laser magnetic resonance (FIR-LMR) spectra due to the CH2F radical have been recorded on seven laser lines at wavelengths between 301 and 568 µm. Observed resonances were assigned to fine and hyperfine components of pure rotational transitions of CH2F in the ground vibrational state and the first excited state of the nu4 out-of-plane bending mode. All assigned transitions obey a-dipole selection rules. The data were combined with previously reported microwave results (Y. Endo, C. Yamada, S. Saito, and E. Hirota, J. Chem. Phys. 79, 1605 (1983)) and subjected to a least-squares fit to determine the parameters of the effective Hamiltonian describing the v4 = 0 and 1 vibrational levels of the CH2F radical. Copyright 1999 Academic Press.

Nanosecond infrared absorption spectrometer

In the present publication, we describe the design details of a time-resolved IR absorption spectrometer with a broadband probe capability and nanosecond time resolution. The IR probe source is based on stimulated electronic Raman scattering in a metal vapor and has a measured pulsewidth of ~1 ns. Broadband collection of the IR light is facilitated by the unique use of a multielement detector array with its associated signal collection circuitry. The spectrometer has been used to record the IR spectra of some gas phase radicals which are indicative of its applicability to spectroscopic and kinetic investigations of short-lived molecular species.