Absolute Surface Coverage Measurement Using a Vibrational Overtone

Published

February 1, 2004

Author(s)

A C. Pipino, J P. Hoefnagels, N Watanabe

Abstract

Sub-monolayer absolute surface number densities are obtained by cavity ring-down spectroscopy (CRDS) for three haloethylenes with differing molecular symmetries on silica using the first C-H stretching overtones. Gas-phase CRDS measurements provide absolute absorption cross sections, while evanescent wave CRDS (EW-CRDS) measurements provide polarized absolute adsorbate spectra. The absolute surface number densities are found from conservation of the integrated band intensities with adsorption along with a measure of surface orientation as derived from the polarization anisotropy. The first stretching C-H overtones of trichloroethylene (TCE), cis-dichloroethylene (c-DCE), and trans-dichloroethylene (t-DCE) occurring around 6050 cm-1 are probed with the idler of a seeded optical parametric amplifier having a 0.075 cm-1 linewidth. The EW-CRDS measurements employ a fused-silica monolithic folded resonator with a peak finesse of .28,500. An independent determination of the absolute surface coverage of TCE on a SiO2 surface is also obtained by mass-spectrometer-based uptake measurements. The sensitivity of EW-CRDS for TCE detection with an unclad resonator is found to be comparable to that obtained with a long-effective-path-length waveguide having a TCE-enriching polysiloxane coating.

Citation

Journal of Chemical Physics

Volume

120

Issue

No. 6

Pub Type

Journals

Keywords

absolute coverage, absolute cross-section, absolute intensity, cavity ring-down, dichloroethylene, evanescent waves, overtones, trichloroethylene, vibrational spectroscopy

Citation

Pipino, A. , Hoefnagels, J. and Watanabe, N. (2004), Absolute Surface Coverage Measurement Using a Vibrational Overtone, Journal of Chemical Physics (Accessed December 22, 2024)