Environmental Analysis

Near-IR Cavity Ringdown Spectroscopy (CRDS): A Powerful Tool for Examining Complex Chemical Mixtures and Reactions

This on-demand presentation will cover the principles of NIR-CRDS spectroscopy. It will discuss various NIR-CRDS spectroscopic apparati available in the laboratory of the author and others and show how specific NIR-CRDS spectra can be observed and analysed.


A difficult challenge for any spectroscopic technique is the observation, characterization, and quantification of a weakly absorbing molecular species in a complex chemical mixture.

The species of interest may be weakly absorbing due to either low concentration or low oscillator strength, or a combination of both.

Complex chemical mixtures have the additional difficulty of interference from typically stronger absorptions from other molecules.

Near-infrared cavity ringdown spectroscopy (NIR-CRDS) offers a powerful tool to solve these challenges.

Observing molecules in an optical cavity offers an increase in net absorption (effective oscillator strength) of the order 106. T

he NIR is a convenient spectral window, lower in frequency that the electronic transitions of many non-reactive molecules and containing only weak combination and overtone vibrational bands.

However electronic transitions of many reactive chemical species fall into the NIR.

The lowest singlet-triplet transitions of molecules are often in this region, e.g. the singlet-triplet transition of O2 which is important in fields as far removed as atmospheric chemistry and photochromatic cancer therapy.

Key oxidation intermediates in combustion often have low-lying electronic transitions, e.g. the peroxy radicals, RO2, where R is any hydrocarbon functional group, like methyl, ethyl, etc.

Atmospheric pollutants, like NO3, likewise have a NIR electronic transition.

This talk will cover the principles of NIR-CRDS spectroscopy. It will discuss various NIR-CRDS spectroscopic apparati available in the laboratory of the author and others. It will show how specific NIR-CRDS spectra can be observed and analyzed.

The audience will learn the principles of cavity ringdown spectroscopy and see working examples of the necessary apparatus and techniques. Near-IR spectra of important molecules will illustrate the advantage of working in this spectral region.


Terry MillerTerry Miller received his undergraduate degree in chemistry from the University of Kansas. After receiving his Ph.D. from Cambridge University, where he was a Marshall Scholar, he went to Bell Laboratories where he became a Distinguished Member of Technical Staff. Thereafter he became the first Ohio Eminent Scholar Professor at The Ohio State University. He has held visiting faculty appointments at Princeton University, Stanford University, and the Institute for Molecular Science in Japan. Dr. Miller's research centers on the spectroscopic identification, characterization and monitoring of reactive chemical intermediates. He has developed numerous spectroscopic techniques spanning frequencies from the microwave to the ultraviolet. Presently, his laboratory focuses upon laser induced fluorescence and cavity ringdown spectroscopy of reactive intermediates, particularly alkoxy and peroxy radicals, involved in the oxidation of hydrocarbons. He is author of more than 350 scientific publications. His research has been recognized with the Meggars Award (Optical Society of America), the Bomem-Michaelson Award (Coblentz Society), the Bourke Medal (Royal Society of Chemistry), the Broida Prize and Plyler Prize (American Physical Society), the Morley Prize (Cleveland Section of the American Chemical Society) and the Ioannes Marcus Marci Medal (Czechoslavak Spectroscopic Society). He has been granted the recognition of Fellow by the American Chemical Society, American Physical Society, Optical Society of America and American Association for the Advancement of Science. He is Editor-in-Chief of the Journal of Molecular Spectroscopy and for 22 years was Chair of the International Symposium on Molecular Spectroscopy which annually attracts approximately 500 conferees. He serves on several other journal editorial boards and conference program committees, including Chair of the International Advisory Committee for the International Free Radicals Symposium. 

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