| Abstract
| - The first and second OH-stretching overtones of HNO3 adsorbed on atomically smooth amorphous SiO2have been probed by evanescent wave cavity ring-down spectroscopy (EW-CRDS) using a broadband high-finesse total-internal-reflection-ring resonator. In contrast to the OH-stretching fundamental, the overtonespectra reveal relatively sharp features under conditions of extensive H-bonding. On the basis of a comparisonwith calculated vibrational frequencies, we find HNO3 exists predominantly as the HNO3−H2O complex onthe surface under ambient conditions. Enabling unparalleled spectroscopic studies of monolayers, thin films,and nanoscale materials, the EW-CRDS technique yields polarized absolute absorption spectra for overtoneand combination transitions at submonolayer coverage. The TIR-ring resonator in particular permits facileexploration of the visible and near-IR regions with a single optical configuration.
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