New electronic spectra of the CHFCl radical observed with resonance enhanced multiphoton ionization

Abstract

The structures and optical spectroscopy of the CHFCl radical and cation were studied by ab initio molecular orbital calculations and by experiment. Ab initio calculations at the MP2/ 6–311++G** theory level found that the optimum structure of the CHFCl+ (X̃ 1A′) cation is planar with r(C–H)=1.092 Å, r(C–F)=1.254 Å, r(C–Cl)=1.599 Å, ∠H–C–F=116.85°, and ∠H–C–Cl=122.14°. CHFCl (X̃ 2A′) radical is nonplanar with r(C–H)=1.083 Å, r(C–F)=1.335 Å, r(C–Cl)=1.705 Å, ∠H–C–F=113.49°, ∠H–C–Cl=116.68°, and ∠F–C–Cl=114.44°. The ab initio angle between the F–C–Cl plane and the C–H bond is Φe=38° and the inversion barrier is Binv=1190 cm−1. Using isogyric reactions to obtain empirical corrections, we calculate IPa(CHFCl)=8.37±0.05 eV. Ab initio vibrational frequencies are reported. The electronic spectrum of the CHFCl radicals was observed between 340–420 nm using one color, mass resolved, 2+1 resonance enhanced multiphoton ionization (REMPI) spectroscopy. The spectrum arises from two-photon resonances with the planar F̃(3p) [λlaser=406.7 nm, ν00=49 160(20) cm−1] and J(3d) [λlaser=361.9 nm, ν00=55 250(20) cm−1] Rydberg states. A third laser photon ionized the radicals. Both states produced the same vibrational constants: ν2 (C–H deformation)=1280(30) cm−1, ν4 (C–Cl stretch)=910(30) cm−1, ν5 (CFCl scissors)=440(30) cm−1, ν6 (OPLA)=980(30) cm−1. The REMPI spectrum exhibited v″6 = 1–6 hot bands of the CHFCl (X̃ 2A) radical. Modeling of these hot bands with a double-well potential gives the inversion barrier, Binv=1180 cm−1, and Φe=42°.