Ultrafast predissociation mechanism of the ¹Π_u 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,o¹Π_u) and four triplet states (C,C′,F,G³Π_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 ¹⁴N₂, prompt predissociation to the continuum of the repulsive C′³Π_u state is facilitated primarily by the b¹Π_u(v = 3)-C³Π_u(v = 9) coupling whereas for ¹⁵N₂ it is the b¹Π _u(v = 4)-C³Π_u(v = 10) coupling term. Predissociation from the F³Π_u and G³Π _u states is important at the higher energies because of their strong coupling to the continuum.