Ultraviolet photolysis of adenine:Dissociation via the 1pi sigma* state

摘要

High resolution total kinetic energy release (TKER) spectra of the H atom fragments resulting from photodissociation of jet-cooled adenine molecules at 17 wavelengths in the range 280>lambda_(phot) >214 nm are reported.TKER spectra obtained at lambda_(phot)>233 nm display broad,isotropic profiles that peak at low TKER (~1800 cm-1) and are largely insensitive to the choice of excitation wavelength.The bulk of these products is attributed to unintended multiphoton dissociation processes.TKER spectra recorded at lambda_(phot) <= 233 nm display additional fast structure,which is attributed to N9-H bond fission on the 1pi sigma potential energy surface (PES).Analysis of the kinetic energies and recoil anisotropics of the H atoms responsible for the fast structure suggests excitation to two 1pi pi* excited states (the 1L_a and 1B_b states) at lambda_(phot) ~230 nm,both of which dissociate to yield H atoms together with ground state adeninyl fragments by radiationless transfer through conical intersections with the 1pi sigma* PES.Parallels with the photochemistry exhibited by other,smaller heteroaromatics (pyrrole,imidazole,phenol,etc.) are highlighted,as are inconsistencies between the present conclusions and those reached in two other recent studies of excited state adenine molecules.