Two-center three-electron bonding in clnh3 revealed via helium droplet infrared spectroscopy: entrance channel complex along the CL + NH3 → CLNH2 + H reaction

Abstract

Pyrolytic dissociation of Cl$_{2}$ is employed to dope helium droplets with single Cl atoms. Sequential addition of NH$_{3}$ to Cl-doped droplets leads to the formation of a complex residing in the entry valley to the substitution reaction, Cl + NH$_{3}$ $\rightarrow$ ClNH$_{2}$ + H. Infrared Stark spectroscopy in the NH stretching region reveals symmetric and antisymmetric vibrations of a C$_{3v}$ symmetric top. Frequency shifts from NH$_{3}$ and dipole moment measurements are consistent with a ClNH$_{3}$ complex containing a relatively strong two-center three-electron (2c-3e) bond. The nature of the 2c-3e bonding in ClNH$_{3}$ is explored computationally and found to be consistent with the complexation-induced blue shifts observed experimentally. Computations of interconversion pathways reveal nearly barrierless routes to the formation of this complex, consistent with the absence of two other complexes, NH$_{3}$Cl and Cl-HNH$_{2}$, which are predicted in the entry valley to the hydrogen abstraction reaction, Cl + NH$_{3}$ $\rightarrow$ HCl + NH$_{2}$