Atmos Gas Cells
The standard long pathlength gas cell range is now the new Atmos™ series of metal-bodied fixed-pathlength gas cells.
They have been optimised using the latest optical modelling tools to give maximum signal-to-noise.
Wide pathlength range (2.5 to 20m) and vacuum to 125 psi operation.
Up to 200 °C with heating jacket and Ni-coated aluminium body.
Gold mirrors (protected) and Viton or Kalrez 'O' ring seals.
CaF2 or ZnSe windows, purgeable transfer optics box and leverlock series baseplate mounting.
Optional features include: vacuum / gas inlet & outlet taps, pressure gauge, desiccant storage caps and purge bellows.
|Base pathlength (mm)||104||139||250||455|
|Number of passes||24||36||40||44|
The Atmos™ range of cells are heatable to 200 °C with the addition of a heating jacket and temperature controller.
- Optimized optical path for unmatched signal-to-noise
- Low cell volume for fast gas exchange
- Ni-coated Al cell bodies for improved thermal transfer from heating jackets. Also holds higher gas pressure than glass.
- Inert stainless-steel mirror substrates and avoidance of glues to prevent outgassing
- 125 psi (8.6 bar) maximum cell pressure
- Retrofittable heating jacket option for up to 200 °C
Which pathlength should I choose?
The absorbance of a gas depends on the distance travelled by the IR light beam through the gas sample. The relationship between absorbance, A, concentration, C, and pathlength, L, is given by Beer’s Law:
A = -log10 (I/I0) = a.C.L
Atmospheric concentrations of gases are usually expressed in C.L units of ppm.m – the number of molecules that would be encountered by the infrared beam across a 1.0 m path.
A gas at 0.1 ppm atmospheric concentration will absorb as much IR light over a pathlength of 100 m as would the same gas at 1 ppm over 10 meters or at 10 ppm over 1 meter.
Accordingly, the pathlength of cell should be chosen to give absorbance values within the spectrometer’s linear range for a given concentration. The following table may be taken as a guide:
|Gas name||formula||v (cm-1)||ppm.m||absorbance|
|C2 to C6 n-alkanes||2960||100||0.1|
|Vinyl chloride||CH2CHCl||950, 900||100||0.06|