Question

In a certain molecule, the transition n → π*(T1) occurs at 385 nm, and the n → π*(S1) transition comes at 356 nm. What is the difference in energy (kJ/mol) between the S1 and T1 states? This difference is due to the different electron spins in the two states.

Answer 1

Energy of T1 (E) = hc/l

   h = planks constant = 6.625*10^-34 j.s

   c = light velocity = 3*10^8 m/s

   l = wavelength = 385 nm = 3.85*10^-7 m

       = (6.625*10^-34*3*10^8/(3.85*10^-7))

       = 5.16*10^-19 joule

Energy of S1 (E) = hc/l

   h = planks constant = 6.625*10^-34 j.s

   c = light velocity = 3*10^8 m/s

   l = wavelength = 356 nm = 3.85*10^-7 m

       = (6.625*10^-34*3*10^8/(3.56*10^-7))

       = 5.58*10^-19 joule

energy difference (DE) = (5.58*10^-19)-(5.16*10^-19) = 4.2*10^-20 juoule/atom.

   = 4.2*10^-20*6.023*10^23 = 25.3 kj/mol