Abstract
Vibrational sum-frequency spectroscopy (VSFS) has been used for some time as a
laboratory-based surface chemical analytical tool. Here, theoretical considerations
in applying the method as a remote-sensing probe for detecting trace levels of
chemicals adsorbed on surfaces are presented. Additionally, a VSFS instrument is
configured to operate at a stand-off distance of 2.2 m using near-nadir incidence
angles. This system was used to measure VSFS spectra for films of pure
1-amino-4-nitrobenzene (<i>p</i>-nitroaniline, PNA) and pure
2-hydroxy-1,3,5-trinitrobenzene (picric acid, PA) adsorbed on polished T-6061
aluminum alloy. These spectra are used to investigate the effect of optical
polarization on the sum-frequency response of these compounds at nadir optical
geometries. Detection limits for each compound are also estimated and found to be
0.51 μg cm<sup>2</sup> for PNA and 0.89 μg cm<sup>2</sup> for PA. The implications
of these results regarding remote sensing applications of VSFS are
discussed.
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