Submillimeter spectroscopy for chemical analysis with absolute specificity

Abstract

A sensor based on rotational signatures in the submillimeter (SMM) region is described. This sensor uses frequency synthesis techniques in the region around 10 GHz, with nonlinear diode frequency multiplication to 210-270 GHz. This provides not only a nearly ideal instrument function, but also frequency control and agility that significantly enhance the performance of the spectrometer as a sensor. The SMM frequencies provide significantly stronger absorptions and broader spectroscopic coverage than lower-frequency microwave systems. Among the characteristics of the sensor are absolute specificity, low atmospheric clutter, good sensitivity, and near-term paths to systems that are both compact and very inexpensive.

THE COMPLETE, TEMPERATURE-RESOLVED EXPERIMENTAL SPECTRUM OF ETHYL CYANIDE (CH3CH2CN) BETWEEN 210 AND 270 GHz

“…Each scan measured the spectral intensity at 25 kHz intervals, with an integration time of ∼15 μs bin −1 and a total scan time of 40 s. The temperature variation over each scan was small enough that the assumption of a constant temperature did not significantly impact the error budget of the experiment. The microwave spectrometer is described in a recent publication (Medvedev et al 2010). Because an analysis of the experimental spectrum, without QM assignment, is the product of this work, it is important that this system not have spurious responses.…”

THE COMPLETE, TEMPERATURE RESOLVED EXPERIMENTAL SPECTRUM OF METHANOL (CH3OH) BETWEEN 214.6 AND 265.4 GHz

“…Each full band scan required 37.7 s. The temperature variation over each scan was small enough that that it did not impact the error budget. The spectrometer is described in more detail in a recent publication (Medvedev et al 2010). It is important that this system not have spurious responses for our complete experimental spectrum (CES).…”

Design and Signature Analysis of Remote Trace-Gas Identification Methodology Based on Infrared-Terahertz Double-Resonance Spectroscopy

“…The spectra measured by IR remote sensing techniques are associated with vibrational modes of constituent intramolecular bonds that must be interpreted in order to identify the analyte. By contrast, molecular rotational spectroscopy in the terahertz (THz)-frequency region reliably identifies the composition in most low-pressure gas mixtures [6], but its detection and recognition specificity at atmospheric pressures is greatly reduced by pressure broadening of the spectral features [7]. A remote sensing methodology based on IR-THz doubleresonance (DR) spectroscopy has been recently shown to overcome these limitations by achieving precise molecular recognition specificity, even discriminating isotopomers, at distances up to 1 km [7,8].…”