Spin exchange rates in proton-hydrogen collisions

نویسندگان

  • Steven R. Furlanetto
  • Michael R. Furlanetto
چکیده

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 K. For kinetic temperatures TK ∼ 100 K, the proton-hydrogen rate coefficient exceeds that for hydrogen-hydrogen collisions by about a factor of two. However, at low temperatures (TK ∼ 5 K) H–H + collisions become several thousand times more efficient than H–H and even more important than H–e collisions.

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Spin-Exchange in Hydrogen-Antihydrogen Collisions

We consider the spin-exchange in ultracold collisions of hydrogen (H) and antihydrogen (H̄) atoms. The cross sections for transitions between various hyperfine states are calculated. We show that the process of spin exchange in H̄ − H collisions is basically driven by the strong force between proton and antiproton, that spin-exchange cross-sections are proportional to the difference of singlet an...

متن کامل

Spin exchange rates in electron-hydrogen collisions

The spin temperature of neutral hydrogen, which determines the 21 cm optical depth and brightness temperature, is set by the competition between radiative and collisional processes. In the high-redshift intergalactic medium, the dominant collisions are typically those between hydrogen atoms. However, collisions with electrons couple much more efficiently to the spin state of hydrogen than do co...

متن کامل

Rates of Acid-Catalyzed NH Proton Exchange of Enaminones, an 1H NMR Study

: 1H NMR spectra of a series of enaminones R-CO-CH=C(NHCH2Ph)-R  [1, R=CH3; 2, R=C6H5; 3, R=CF3; 4, R=CH2CH2CH2; 5, R=CH2C(CH3)2CH2], were obtained in the presence of trifluoroacetic acid in CDCl3 or DMSO-d6 at 28 °C. S...

متن کامل

Measuring fast hydrogen exchange rates by NMR spectroscopy.

We introduce a method to measure hydrogen exchange rates based on the observation of the coherence of a neighboring spin S such as (15)N that has a scalar coupling J(IS) to the exchanging proton I. The decay of S(x) coherence under a Carr-Purcell-Meiboom-Gill (CPMG) multiple echo train is recorded in the presence and absence of proton decoupling. This method allows one to extract proton exchang...

متن کامل

Studies on the SPEEK membrane with low degree of sulfonation as a stable proton exchange membrane for fuel cell applications

Sulfonated poly (ether ether ketone) (SPEEK) with a low degree of sulfonation (DS = 40%) was prepared for proton exchange membrane fuel cells (PEMFC). Poly (ether ether ketone) (PEEK) was sulfonated in concentrated H2SO4 under N2 atmosphere and characterized by the hydrogen nuclear magnetic resonance (H-NMR) technique. After preparation of the SPEEK polymer, the obtained polymer was dissolved i...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 2007