Dear Sohail,

what energy of H2+ are you talking about ??, i guess its low energy within 10-100 KeV. is it ??

As I saw in the experiments effective reactions between metallic atoms and H2+ practically absent - in the spectra are not present components MHn. Besides in discharge with addition of 0.3% H2 the intensity of H2+ is very low. In spetrum presents very intense H3+ and low H4+ and H5+ components. 

But molecular hydrogen can participate in differet reactions with molecular ions. The intensities of gas components can be reduced by introducing small amounts of hydrogen (0.3—0.5%) into the discharge gas. In this case, a number of reactions begin in the afterglow, which lead to charge transfer from some gas components mainly to H3+.

Ar+ +H2– ArH+ + H

ArH+ + H2 – Ar + H3+

Ar2+ +H2– Ar2H+ + H

Ar2H+ + H2 – 2Ar + H3+

OH+ + H2 – OH2+ + H

OH2+ + H2 - OH3+ + H

OH3+ + H2 – OH2 + H3+

H2+ + H2 – H3+ + H

H3+ + H2 – H4+ + H

H4+ + H2 – H5+ + H

COH+ + H2 – COH2+ + H

Reactions (2)—(12) cause the intensities of the gas

eous components to be reduced by one or two orders

of magnitide, whereas the intensities of the analyte com

ponents increase by 1.5 to 2 times. The use of hydro

gen additive allows one to considerably decrease some

interference, in particular, Ca in silicon samples can

be detected by the major isotope 40Ca. Also, hydrogen

causes a decrease in the Ar+ and ArH+ signal intensi

ties and thus significantly reduces the scattered ion intensities.

See: Russian Chemical Bulletin, International Edition, Vol. 61, No. 4, pp. 752—767, April, 2012

Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 0748—0764, April, 2012.

10665285/12/61040752 © 2012 Springer Science+Business Media, Inc.

Analytical glow discharge mass spectrometry

A. A. Ganeev, A. R. Gubal, K. N. Uskov, and S. V. Potapov

Dear Ganeev, 

Thanks for your detailed reply.

Ganeev  "in discharge with addition of 0.3% H2 the intensity of H2+ is very low."

SM - I think the major contribution in the formation of hydrogen molecular ions in Ar/H2 discharges comes mainly from the charge transfer process involving argon ions such as 

Ar+ (3p5 2Po1/2, 3/2) + H2 (X 1Σg+) → H2+ (X 2Σg+ υ´) + Ar + ΔE

Other processes such as direct electron impact ionization or two step ionization from hydrogen molecular metastable states can also be contributed. However, in Ar + 0.3% H2 discharge, with such higher concentration of hydrogen, the population of argon ions, which are mainly responsible for the formation of H2+ are quenched significantly. Therefore, it is expected that the signal of H2+ ions should be low. 

Ganeev "The intensities of gas components can be reduced by introducing small amounts of hydrogen (0.3—0.5%) into the discharge gas. The intensities of the gaseous components to be reduced by one or two orders of magnitude, whereas the intensities of the analyte components increase by 1.5 to 2 times."

SM - I agree with you and we have also experimentally observed this. In literature search, various people have reported reasonable explanations for the decrease in the intensities of the gaseous components, however, I could not find any explanation for the increase of analyte ions in Ar/H2 discharges. 

Now it is widely known that the presence of hydrogen in argon GD results in the quenching of argon ions, argon metastable, electron density, and also sputter rate of analyte. In that case, the increase of analyte ions in Ar/H2 becomes more interesting. 

In the regard of above scenario, I propose that there must be some additional plasma processes which are responsible for this and collision of H2+ ions with metallic atoms could be responsible for this, particularly at the presence of lower hydrogen concentrations in argon plasmas. 

Dear Sohai Mushtaq. I think that H2+ ions can not play a significant role in increasing the intensity of the elements of the sample. The fact that an increase in the intensities of the elements is non-selective process. Intensities of all elements increase approximately the same. The direct effect of H2+ ions is possible via an asymmetric charge transfer. In this case there was a notable change to the relative intensities of the sample components. In addition, the intensity of the H2+ ions is very low - 200-400 times lower than that of H3+ ions for different types of the sample, so the probability of the process H2+ + M – M+ + H2 is small. If you will send me your E-mail – I will send you the spectra with hydrogen components (In this format, the file size is limited). My E-mail: [email protected].

To my mind the increase in intensity is due to the increase in the concentration of metastable argon atoms. However, the mechanism of increasing the concentration of these atoms is not yet clear.

Best wishes,

Alexander

Dear Ganeev, 

Please send me the files at this email address - [email protected]

What is the lowest concentration you used for Ar/H2 mixture?

Thanks,

SM

My initial interpretation was also same that increase in metastable states would be involved here. However, in literature there are reasonable evidences that the presence of hydrogen results the quenching of argon metastable states. Furthermore, for Ar/H2 mixtures, using the dc GD-TOFMS at constant voltage and pressure conditions, Menéndez also reported that though there are reduced sputtering rates for analyte but still there are higher sensitivities for analyte ions in argon/hydrogen mixtures than in pure argon plasmas which again negate this argument that increase in analyte ion signals in argon/hydrogen signal is due to increase of argon metastable atoms.

A. Menéndez, R. Pereiro, N. Bordel and A. Sanz-Medel, “H2/Ar direct current glow discharge mass spectrometry at constant voltage and pressure”, Spectrochim. Acta Part B, 2005, 60, 824-833

A. Bogaerts, “Computer simulations of argon-hydrogen Grimm-type glow discharges”, J. Anal. At. Spectrom., 2008, 23, 1476-1486

S. Mushtaq, E. B.M. Steers, J. C. Pickering, T. Gusarova, P. Šmid and V. Weinstein, “Effects of traces of oxygen on Grimm-type glow discharges in argon”, J. Anal. At. Spectrom., 2011, 26, 766-775.

M. H. Gordon and C. H. Kruger, “Nonequilibrium effects of diluents addition in a recombining argon plasma”, Phys. Fluids B, 1993, 5(3), 1014-1023.