An absorbing species R is monitored in an IRS experiment featuring a forward step in which species is reduced to R at the diffusion-controlled rate, and a reversal step in which R is converted back to O, also under diffusion control. Show that the normalized absorbance is given by d(t < )() = 1 - exp(a2 0 erfc(af1/2) s&(t > )() = exp[a\t - r)] erfc[a(f - ) ] where r is the forward step width and a = 2 /8. Assume that r is large enough that (17.1.14) applies. For simplicity, you may assume Do = DR = D. How many parameters are needed to fit the transient? Plot points for about 10 values of tlr in the range 0 < t/ < 2.