Rotational spectroscopy is introduced as a new in situ method for monitoring gas-phase reactants and products during chemical reactions. Exploiting its unambiguous molecular recognition specificity and extraordinary detection sensitivity, rotational spectroscopy at terahertz frequencies was used to monitor the decomposition of carbonyl sulfide (OCS) over an aluminum nanocrystal (AlNC) plasmonic photocatalyst. The intrinsic surface oxide on AlNCs is discovered to have a large number of strongly basic sites that are effective for mediating OCS decomposition. Spectroscopic monitoring revealed two different photothermal decomposition pathways for OCS, depending on the absence or presence of H2O. The strength of rotational spectroscopy is witnessed through its ability to detect and distinguish isotopologues of the same mass from an unlabeled OCS precursor at concentrations of <1 nanomolar or partial pressures of <10 μTorr. These attributes recommend rotational spectroscopy as a compelling alternative for monitoring gas-phase chemical reactants and products in real time.
Bibliographical noteFunding Information:
The authors thank C. Neese and M. Reish for discussions regarding rotational spectroscopy, J. Yang, A. Alabastri, and P. Nordlander for discussions regarding photothermal heating of the Al NCs in vacuo, and Hossein Robatjazi for the instrument schematic in Figure 1a. This work was funded by the Air Force Office of Scientific Research Multidisciplinary Research Program of the University Research Initiative (AFOSR MURI FA9550-15-1-0022), the Army Research Office (MURI W911NF-12-1-0407), Defense Threat Reduction Agency (HDTRA 1-16-1-0042), the Army Aviation and Missile RD&E Center In-house Laboratory Innovative Research program, and the Welch Foundation under grant C-1220 (N.J.H.). D.F.S. acknowledges the National Science Foundation for a Graduate Research Fellowship under grant no. 1450681.
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- aluminum nanocrystals
- carbonyl sulfide
- rotational spectroscopy