3 ms·
That was also my first reaction. But TFA says that H+ reacted with neutral He. That gives you HeH+, which is what they detected. And I see that the ionization
by mirimir 8y ago
That was also my first reaction.
But TFA says that H+ reacted with neutral He. That gives you HeH+, which is what they detected. And I see that the ionization energies of He are 2372.3 kJ/mol for the first electron, and 5250.5 kJ/mol for the second. But the ionization energy of H is just 1312.0 kJ/mol. So neutral He would have formed long before neutral H, and He plus H+ was the first possible combination.
Also, HeH+ is an extremely strong acid, so it would grab an electron from just about anything else that it encountered.
And neutral HeH is not stable.
- ridgeguy 8y agoThanks, I forgot this is an ionized species (the + charge). That can change kinetics a lot.
- logfromblammo 8y agoIn the post-bang environment, you can flip those numbers around to see the order in which the hot nuclei capture the hot electrons. A [He+2] nucleus can grab hotter electrons than a [He+1] ion, which in turn can grab hotter electrons than a [H+] proton. So at a temperature cool enough for neutral He to exist and still hot enough for [H+] ions, they were pretty much the only massive things around that could react with each other. If an [HeH+] caught a hot electron, it would fall apart into He and H, with no further need to share electrons. A [H+] could glom onto that neutral H to make [H2+] (which also forms when cosmic rays blast through an H2 cloud). If an [H2+] caught another electron, the H2 and another [H2+] will react to make [H3+] and H. So it turns out [H3+] is a pretty common hot cloud molecule, too. Plain old H2 doesn't exist by itself until the temperature drops enough for those positive ions to catch electrons and stop being an acidic plasma.