Vibrational relaxation of fluorine by a shock tube schlieren method

The vibrational relaxation of fluorine in argon has been studied in the temperature range 500–1300°K behind incident shock waves. A laser schlieren system utilizing a fast, quadrant photodiode and difference amplifier was used to record density changes behind the shock waves. Data from 10% and 20% fluorine in argon mixtures were reduced to relaxation times using the Blackman technique and relaxation times for pure fluorine, and fluorine infinitely dilute in argon deduced using a curve fitting technique. The fluorine-fluorine and fluorine-argon relaxation times, in μsec · atm, were found to be best described by ln(Pτ)F2–F2 = −6.972+65.20T−1/3,ln(Pτ)F2–Ar = −8.650+96.97T−1/3,where T is the temperature in degrees Kelvin. The results of this investigation agree well with the low temperature results of Shields for pure fluorine relaxation.