Can you elaborate your experimental setup a little bit more, please?

There could be something degasing from you chamber walls for example - how good is the wavelength calibration of your optical spectrometer?

do yo have molecular or atomic hydrogen (or do you know, which one is the dominant species in your experiment)?

Dear Sir,

Can you elaborate your experimental setup a little bit more, please?

A standard microwave plasma reactor used in our tests incorporates a microwave generator having power supply up to 6000 W. A magnetron is used to produce electromagnetic waves of the standard microwave frequency of 2.45×109 Hz which are employed to produce plasma of high power densities. These microwaves are guided to the chamber with the help of a wave guide, where it interacts with the incoming hydrogen gas (99.999% pure) to produce hydrogen plasma. The hydrogen plasma interacts with hematite ore (Fe2O3) to produce Fe and H2O.

There could be something degasing from you chamber walls for example

There is evolution of water as reaction product from the pellet after hydrogen plasma interacts with the surface.

- how good is the wavelength calibration of your optical spectrometer?

It is a calibrated OES.

do you have molecular or atomic hydrogen (or do you know, which one is the dominant species in your experiment)

Please find herewith emission spectra for your kind reference. The 589 line matches with sodium line BUT Sodium is not present in our experiment

Awaiting your response,

Best regards,

Sabat

ok, I assume you have already substracted a dark measurement from your spectrum to avoid things like defect pixels (what can be a rare occurence) or some stray light from any Sodium light sources in your laboratory? - the spectrum is quite small, so I cannot see much details...

do you have some glass windows or glasses which are in contact with your plasma? - if yes, what kind of glass is it?

Dear Sir,

No 589 line is found when I run the experiment with hydrogen plasma (WITHOUT SAMPLE). BUT when I run the experiment with sample (Fe2O3), the 589 line is seen.

In both cases (with & without sample), the glass window is there. So I don't think glass window has any effect. Anyway, glass window is not in contact with plasma.

When the Fe2O3 sample is exposed to hydrogen plasma, the following reaction takes plase

Fe2O3+Hydrogen plasma=Fe+H2O

So there is evolution of H2O vapour.

Is the 589 line related to water vapour or hydrogen burning?

Best regards,

Sabat

that's why I asked about the quality of your calibration - if you have up to one or two wavelengths error, you can easily end up with a wavelength of a wrong substance.

Dear Sir,

I am using 2 OES instruments. One is inbuilt with microwave machine and other one I attach to glass window of microwave setup. Both of hem are giving the same result.

So the question of calibration doesn't arise.

I feel that the 589 line may be related to water vapour or hydrogen burning.

What do you say in this regard?

Best regards,

Sabat

My guess would be the iron, just as Tsanko Tsankov said - there are a whole bunch of them at around 689 nm.

You just can check out online databases or books for the lines of H2O.

Is the only line without identification? The wavelength is not sufficient criteria for identification, especially with so low precision. For more accurate wavelength determination the calibration of the spectrometer is required. Also the spectrometer should have sufficient resolution.

Dear Andrei,

The above pdf file "Emission Spectra" consists of 60 spectra from t = 1min to t = 60mins.

Also iron is not present.

Is the 589 line related to water vapour or hydrogen burning?

What do you think?

Regards,

Sabat

This spectrum has a too low resolution to make any species identification.

Nevertheless, I would question your statement that no sodium is present. Your plasma torch has very high power densities and only impurities of sodium from your "pure Fe2O3" sample will lead to significant emission in the plasma. I have observed in the past sodium and potassium lines emission in a 100W microwave plasma torch created in argon inside a ceramic tube at atmospheric pressure. The Na I and K I lines were coming from the ceramic tube. So with 6kW, you can expect anything to appear in your plasma emission spectrum.

The spectra of hydrogen (both atomic and molecular) and water are rather well documented in the litterature. A quick look at some papers should help you to find out their characteristics...

Dear Emile,

Thank you very much.

Can you please suggest/send some reference?

Regards,

Sabat

I support the answer of Emile. Low resolution does not allow to make safe identification very often. An example of sodium emission from ceramic is attached, see fig.5.

First guess for the spectrum: Na 589, H alpha 656 and

The water vapors can appear in emission as OH radical at 306-315 nm.

A safe identification require additional efforts...

I couldn't find the pdf file with the spectrum. However, the 589 nm line could be the second order line (~294.5 nm) of your spectrometer. Iron has many emission lines in the ~395 nm spectral range. You can check for any second order lines in your spectrum.

I think it could be a Na I line.This line is very intense and often emitted by plasmas generated inside quartz tubes (we detected it in MW surface-wave plasmas using power as low as 150 w). If so, you should be able to see another Na I line at 589.6 nm.

In atomic emission spectrum of sodium, Na I 588.995 nm is one of the intense resonance lines with upper energy level 2.104 eV. There is another Na I resonance line 589.592 nm with upper energy level 2.102 eV as also mentioned by Prof. Baig in his comment, however, it is quite difficult to resolve these lines unless one have instrument with good resolving power. In addition, there are no Na I lines with reasonable S/N ratio in 200-900 nm spectral region which can support the confirmation of sodium here. Therefore, uncertainty regarding Na still prevails here.

In previous comments from Mr. Sabat, it is important to note that No 589 line is found when he runs the experiment with hydrogen plasma (WITHOUT SAMPLE). BUT when he runs the experiment with sample (Fe2O3), the 589 line is seen. There are 31 Fe I lines within 588.0-590.9 nm spectral region from different upper energy levels and it is quite possible that hydrogen results in selective excitation of one of the iron atomic lines. It could be interesting to run with another gas and see the behaviour of emission intensities in that region. Good luck!!!

Thank you Sohail for your beautiful review. You are absolutely right.

BUT this 589 line is really confusing me......

It never leaves my oxides..

This confusing line is also present when I run experiments with other oxides!!!!!!!!!.