ISOTOPE EFFECTS IN RADIATIVE COOLING - THE AL(C6H6)(+) SYSTEMS

At 300 K the low pressure association reactions of Al+ with C6H6, C6H5 D, [1,3,5]-C6H3D3, and C6D6 have been studied by using Fourier transfo rm ion cyclotron resonance (FTICR) mass spectrometry. Several rate con stants were found to correlate with the deuterium content of the benze nes. For example, radiative association (k(ra)) correlates with the co ntent of D atoms, ranging from 1.7 x 10(-12) (for C6H6) to 6.2 x 10(-1 2) cm(3) molecule(-1) s(-1) (for C6D6). IR photon emission (k(t)) occu rs With a rate constant varying from (17 +/- 5) s(-1) (C6D6) to (24 +/ - 7) s(-1) (C6H6). Rate constants (k(r)) for the unimolecular dissocia tion of the chemically activated collision complexes back to reactants range from (3 +/- 1) x 10(3) s(-1) (C6D6) to (16 +/- 5) x 10(3) s(-1) (C6H6). Ab initio molecular orbital calculations and equilibrium meas urements were used to assess a bond dissociation energy of BDE(Al+-(C6 H6))=39.0 kcal mol(-1), and equilibrium measurements indicate BDE(Al+- (C6D6)) > BDE(Al+(C6H6)).