Open AccessSpin exchange rates in proton–hydrogen collisions
Author(s) -
Furlanetto Steven R.,
Furlanetto Michael R.
Publication year - 2007
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2007.11921.x
Subject(s) - physics , hydrogen , proton , atomic physics , radiative transfer , spin (aerodynamics) , hydrogen line , range (aeronautics) , spin isomers of hydrogen , nuclear physics , thermodynamics , quantum mechanics , materials science , composite material
The spin temperature of neutral hydrogen, which determines the optical depth and brightness of the 21‐cm line, is determined by the competition between radiative and collisional processes. Here, we examine the role of proton–hydrogen collisions in setting the spin temperature. We use recent fully quantum‐mechanical calculations of the relevant cross‐sections, which allow us to present accurate results over the entire physically relevant temperature range 1–10 4 K . For kinetic temperatures T K ≳ 100 K , the proton–hydrogen rate coefficient exceeds that for hydrogen–hydrogen collisions by about a factor of 2. However, at low temperatures ( T K ≲ 5 K) H–H + collisions become several thousand times more efficient than H–H and even more important than H–e − collisions.