Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: hamdani yusuf on 25/05/2016 11:12:58
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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?
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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.
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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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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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But this picture doesn't seem to agree with your statement above
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fimages.slideplayer.com%2F28%2F9359202%2Fslides%2Fslide_22.jpg&hash=d10de123add32331f1b2f083e5a80e18)
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Under the right conditions there are visible emissions from molecular species.
http://rsta.royalsocietypublishing.org/content/370/1978/5028