A commercial molecular gas cracker for the production of O(3P) atoms has been used to dope helium nanodroplets. On the basis of mass spectrometry results, we estimate that with optimal conditions, 26% of the droplet ensemble is doped with single oxygen atoms. Upon sequential capture of an O(3P) atom and HCN, a weakly bound complex is observed via measurements of beam depletion in the CH stretching region of the IR spectrum. The analysis of rotational fine structure and comparisons to ab initio computations support an assignment of a band centered at 3285.89 cm-1 to a linear, H-bound, (3Σ) O−HCN van der Waals complex. There is no experimental evidence for the production of an N-bound complex. Multi-reference ab initio computations predict a relatively small barrier for interconversion from the higher energy N-bound complex to the more stable H-bound system. The HCN + O(3P) results presented here demonstrate the feasibility for analogous alkene + O(3P) spectroscopic studies, in which O(3P) and alkenes of varying substitution are combined in helium droplets via the sequential capture scheme. As the real reaction barrier (i.e. for the ethene and propene reactions) evolves to being submerged below the asymptotic limit (i.e. for the butene reactions), one might expect that strongly bound reaction intermediates, such as triplet biradicals, will be observed in helium droplets, rather than van der Waals complexes. Given the fact that a 10,000 atom helium droplet can dissipate 140 kcal/mol, it should be possible to quench the internal energy of these reaction intermediates and probe them for the first time spectroscopically.

O(3P) + alkene chemistry in helium nanodroplets

255th National Meeting (2018)

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