Sequential Capture of O(³P) and HCN by Helium Nanodroplets: Infrared Spectroscopy and ab Initio Computations of the ³Σ O–HCN Complex

Abstract

Catalytic thermal cracking of O is employed to dope helium droplets with O(P) atoms. Mass spectrometry of the doped droplet beam reveals an O dissociation efficiency larger than 60%; approximately 26% of the droplet ensemble is doped with single oxygen atoms. Sequential capture of O(P) and HCN leads to the production of a hydrogen-bound O-HCN complex in a Σ electronic state, as determined via comparisons of experimental and theoretical rovibrational Stark spectroscopy. Ab initio computations of the three lowest lying intermolecular potential energy surfaces reveal two isomers, the hydrogen-bound (Σ) O-HCN complex and a nitrogen-bound (Π) HCN-O complex, lying 323 cm higher in energy. The HCN-O to O-HCN interconversion barrier is predicted to be 42 cm. Consistent with this relatively small interconversion barrier, there is no experimental evidence for the production of the nitrogen-bound species upon sequential capture of O(P) and HCN.

Chemistry and physics of dopants embedded in helium droplets

“…The splitting of stable molecules results in the formation of at least two fragments. Only in rare cases, these fragments are the radicals of interest as in the case of doping of helium droplets with Cl, Br, and I atoms, formed by thermal dissociation of Cl 2 , Br 2 , and I 2 (Merritt et al, 2005) or when O 2 is dissociated to produce O atoms (Brice et al, 2017). In other cases, the second fragment is an unwanted contaminant.…”

Cold and controlled chemical reaction dynamics

“…162 This enables one to study the formation of collision complexes and to probe transient intermediates. In this way, the sequential capture of reactants has facilitated a detailed study of the O-HCN complex formed by the O( 3 P) + HCN reaction, 167 and of the ethylperoxy radicals (CH 3 CH 2 OO) formed following CH 3 CH 2 + O 2 collisions within a He droplet (see Fig. 5).…”