How Can DC Electrostatic Fields Ionize Molecular Hydrogen?

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Discussion Overview

The discussion centers around the ionization of molecular hydrogen (H2) using DC electrostatic fields and alternative methods such as multiphoton ionization and microwave radiation. Participants explore the energy requirements for ionization and practical approaches to achieve it, while considering the implications of different ionization techniques.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant inquires about converting ionization energy from kJ/mol to a measure of electrostatic field strength, questioning whether using eV would simplify this conversion.
  • Another participant asserts that electric fields cannot be directly converted to energy and emphasizes the need to calculate the probability of ionization in a given field, mentioning tunnel ionization.
  • A participant asks for practical methods to ionize H2, suggesting microwaves as a potential approach.
  • In response, it is noted that strong microwave radiation would be necessary, as the ionization energy cannot be overcome by microwave photon energy alone.
  • One participant seeks recommendations for effective and energy-efficient methods to ionize small volumes of hydrogen gas, specifically asking about the energy requirements for multiphoton ionization.
  • Another participant explains that multiphoton ionization can occur with lower energy photons, as long as multiple photons combine their energy to exceed the ionization threshold, highlighting the importance of light intensity and laser parameters.
  • Further, it is mentioned that one-photon ionization requires photons with energy exceeding the ionization potential, which necessitates working in the XUV range and using vacuum conditions to avoid photon absorption by air.
  • A historical reference is made to studies on the H2+ molecular ion, suggesting that electric discharge is a common method for producing ions, and noting the relative ease of generating 15 eV electrons compared to photons.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of using DC electrostatic fields for ionization, with some suggesting alternative methods like multiphoton ionization and microwave radiation. The discussion remains unresolved regarding the most effective and energy-efficient approach for ionizing H2.

Contextual Notes

Participants discuss various assumptions regarding energy requirements and the conditions necessary for different ionization methods, including the limitations of electric fields and the need for specific photon energies. The conversation reflects a range of experimental approaches without reaching a consensus on the best method.

Who May Find This Useful

This discussion may be of interest to researchers and students in the fields of chemistry and physics, particularly those exploring ionization processes, experimental techniques, and the behavior of molecular hydrogen in electric fields.

Misha Kuznetsov
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The ionization energy of H2 is 1488 kJ/mol. How strong of a DC electrostatic field would be need to ionize H2 molecules all at a distance 'd' from the source of the field? What I am asking is how to convert the known unit (joule) into a measure of an electrostatic field since electric fields are expressed in Newtons per coulomb or volts per meter.

Would this be easier to do if the ionization energy was in eV rather than in joules? (It is approximately 15.4 eV)

I need to know how to do this for a personal project, not for homework.

Thank you.
 
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You can't convert the electric field to an energy. You have to calculate the probability of ionization for the molecule placed in a given electric field. See tunnel ionization.

As far as I know, there is no way you can create in practice a DC field strong enough to actually ionize H2.
 
In that case, what would be a practical way to do it? I read something about using microwaves, could that work to do it?
 
If what you read seems trustworthy, that is it presents experimental data, then it worths a try. Just one thing for sure, you will need a system that is able to produce very strong microwave radiation because the ionization energy you mentioned above cannot be overcome by photon energy of microwave field.
 
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Can anyone recommend a way to ionize very small volumes of hydrogen gas that is both effective, and more importantly, not too energy consuming? By small volume, I mean no more than a few hundred molecules at STP. In the case of multiphoton ionization, does each photon have to have lots of energy?
 
Misha Kuznetsov said:
In the case of multiphoton ionization, does each photon have to have lots of energy?
On the contrary, multiphoton ionization takes place when photon energy (## \hbar \omega ##) is less than ionization energy. Therefore it takes multiple of photons for them to add up their individual energy so that the sum can surpass the ionization energy. However the ionization rate of multiphoton ionization strongly depends on the light's intensity, that's why when using laser, short pulse and tight focusing are required.

One photon ionization is another way to ionize thing as long as one photon energy is sufficient to exceed the ionization potential, in the case of 15.4 eV potential you need to provide radiation within XUV range. However working in UV region down to shorter wavelengths requires evacuating the system (such as using vacuum chamber) because air molecules heavly absorbs photons with short wavelengths.
 
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Misha Kuznetsov said:
Can anyone recommend a way to ionize very small volumes of hydrogen gas that is both effective, and more importantly, not too energy consuming? By small volume, I mean no more than a few hundred molecules at STP. In the case of multiphoton ionization, does each photon have to have lots of energy?

In the olden olden days, people studied H2+ molecular ion. Looking at Herzberg's Diatomics yields: H. Beutler and H. O. Juenger, Z. Physik 101, 304 (1936); O. W. Richardson, Proc. Roy. Soc. London 152, 503 (1935); O. W. Richardson, Nuovo cimento, 15, 232 (1938).

A very nice review article on the spectroscopy of molecular ions has references for experimental work on H2+ as well as HD+. The original papers will describe how they produced the ions -- generally an electric discharge is used to produce the ions (electron impact ionization). It is very difficult to make ca. 15eV photons, but not so hard to make 15eV electrons with which to ionize the H2.

http://www.cchem.berkeley.edu/rjsgrp/publications/papers/1980-1983/13_saykally_1981.pdf
 
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