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Author Topic: What determines the spectrum produced by hydrogen?  (Read 717 times)

Offline hamdani yusuf

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What conditions (temperature/pressure) determine whether hydrogen gas will produce atomic or molecular spectrum ?
Does the transition happens gradually or is there a distinct limit?
« Last Edit: 25/05/2016 19:58:45 by chris »


 

Offline agyejy

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Re: What determines the spectrum produced by hydrogen?
« Reply #1 on: 25/05/2016 23:42:44 »
The atomic spectrum is generally only visible when the atomic hydrogen is present which generally means that the molecular hydrogen you started with has dissociated. There are various combinations of temperature and pressure at which the dissociation would occur. Generally speaking by increasing the pressure you could increase the temperature at which the molecular hydrogen remains stable. I'm relatively sure some plasma physicists working on fusion as mapped this all out in a phase diagram. Unfortunately all I can find on google is phase diagrams concerning metallic hydrogen which don't really show the area you're interested in very well.
 

Offline lightarrow

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Re: What determines the spectrum produced by hydrogen?
« Reply #2 on: 31/05/2016 12:45:53 »
Usually molecular transitions have much lower energy than atomic transitions, so if you excite with an electric discharge the ordinary molecular hydrogen, you will find line emissions of the atomic spectrum, together with line emissions of the molecular, but these last are almost in the infrared so if you look at the visible + UV part of the spectrum, you will find only atomic lines.

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lightarrow
 

Offline hamdani yusuf

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Re: What determines the spectrum produced by hydrogen?
« Reply #3 on: 31/05/2016 14:42:11 »
Usually molecular transitions have much lower energy than atomic transitions, so if you excite with an electric discharge the ordinary molecular hydrogen, you will find line emissions of the atomic spectrum, together with line emissions of the molecular, but these last are almost in the infrared so if you look at the visible + UV part of the spectrum, you will find only atomic lines.

--
lightarrow
But this picture doesn't seem to agree with your statement above
 

Offline Bored chemist

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Re: What determines the spectrum produced by hydrogen?
« Reply #4 on: 31/05/2016 14:44:25 »
Under the right conditions there are visible emissions from molecular species.
http://rsta.royalsocietypublishing.org/content/370/1978/5028
 

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Re: What determines the spectrum produced by hydrogen?
« Reply #4 on: 31/05/2016 14:44:25 »

 

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