Infrared Gas Analyzer: How to Accurately Measure Concentration

[Charles123]

An infrared gas analyzer gives you the concentration of a given molecule that absorbs radiation in a specific infrared band, in a gas, by determining the attenuation of radiation of the frequency in case, when in a path between emitter and receiver is a sample of the gas in analysis. My question is, since the molecule will re-emit the radiation, and it can do this in any direction, some of it can reach the receiver. Therefore, in order to not account for this radiation, that would otherwise indicate a minor concentration of the molecule, what is done? Is it just a question of time lag of the re-emitted radiation in comparison to the radiation that reaches the receiver directly?
Thank you
Regards

 

[CWatters]

I don't know for sure how its done but the radaition spectra has a different intensity pattern to the absorption spectra.

Appears they are quite complex devices..
http://en.wikipedia.org/wiki/Infrared_gas_analyzer

 

[mikeph]

It's very unlikely the molecule will return to its original state, and also that any radiated light is oriented directly at the detector, so the signal will be tiny.

Stimulated emission is a much bigger effect, where the light can make a molecule emit an identical photon in the same direction as the original one. Even so, this effect is very small in the infrared (~0.01% I think).

 

[Charles123]

Thank you for your answers!
CWatters, even that is the case, it can still be emission in the same wavelength, isn`t that the case?
"It's very unlikely the molecule will return to its original state", why is that MikeyW?
Regards