Ultrafast predissociation mechanism of the 1Πu states of 14N2 and its isotopomers upon attosecond excitation from the ground state.

The computed time evolution of excited electronic and nuclear states of dinitrogen following a broad laser pulse excitation of the dipole allowed singlet Π states is discussed. The computations use two complementary methods to solve the time-dependent Schrödinger equation of the molecule. The electronic evolution is described as spanning seven states, the three dipole-allowed singlet states (b,c,o(1)Π(u)) and four triplet states (C,C',F,G(3)Π(u)). Spin-orbit coupling mixes states of the two manifolds. The computed dynamics includes the attosecond pulse single photon pumping from the electronic ground state. The ultrafast exit to the continuum from the bound states that are optically excited and the large isotope effect on this process are used as a probe of the electron dynamics as coupled to the onset of the nuclear motion. For (14)N(2), prompt predissociation to the continuum of the repulsive C'(3)Π(u) state is facilitated primarily by the b(1)Π(u)(v = 3)-C(3)Π(u)(v = 9) coupling whereas for (15)N(2) it is the b(1)Π(u)(v = 4)-C(3)Π(u)(v = 10) coupling term. Predissociation from the F(3)Π(u) and G(3)Π(u) states is important at the higher energies because of their strong coupling to the continuum.