[fiendofbooks]

I'm reading an article (J. Phys. Chem A, 2011, 115, 3335) on the kinetics of atmospheric OH oxidation of ethanol (and it's various isotopomers). I understand that k' is used to designate pseudo-first order kinetics reactions. But halfway through the paper the authors switch to kappa as the designation for the rate constant. Is there a standard reason for using kappa? How is it different from k and k'?

Thanks!