Ultrafast field induced dynamics of Coherent States

In a standard notation a coherent state is a specific combination of the vibrational levels of the harmonic oscillator. They are also referred as Glauber states, quasi-classical states and eigenvectors of the creation operator a (Cohen-Tannoudgi, V1, p. 559). In what follows we use this term only because of qualitative similarity of the quasi-classical states to the wave packets pumped during ultrafast excitation.

In our notation a coherent state — is a coherent superposition of vibrational or/and electronic states, however the coefficients in this superposition are dictated by the exact ultrafast field-induced dynamics. If the duration of the pulse is short compare to the vibrational period of the excited state potential - there is not enough time for the pumped wave packet to sample the phase-space. Instead of specific vibrational eigenstate, as common in the CW experiments, during an ultrafast excitation a coherent superposition of states is pumped to several electronic states. The dynamics induced by the pulse has a well-defined origin in time, and also in coordinate representation - as the excited wave packets are localised in the Franck-Condon region. This makes a perfect ground for the time-domain picture of the photo-chemical reaction dynamics.

In what follows we study the ultrafast field-induced dynamics in the manifold of singlet states with bound (N2) and dissociative (LiH,LiF) potentials. The singlet-triplet coupling is weak therefore one needs to model a longer time-scale dynamics. We used N2 as an example, because its photodissociation (that goes from initially excited bound singlet states through the S-T coupling to the bound and dissociative triplets) is widely studied both using high-resolution spectroscopy and high-level ab initio Quantum Chemistry.

Singlet-singlet non-radiative transfer for the coherent states in diatomics:

Correlated electron-nuclear motion during non-adiabatic transitions in LiH and its isotopomers. J. Phys. B: At., Mol. Opt. Phys. 53, 134001 (2020)

Time-dependent view of an isotope effect in electron-nuclear nonequilibrium dynamics with applications to N2. PNAS, 115 (23), 5890-5895 (2018)

Propagation of nonstationary electronic and nuclear states: attosecond dynamics in LiF. Mol. Phys., 116 (19-20), 2524-2532 (2018)

On the fly quantum dynamics of electronic and nuclear wave packets. Chem. Phys. Lett., 699, 155-161 (2018)

Intersystem crossing of the coherent states:

Time resolved mechanism of the isotope selectivity in the ultrafast light induced dissociation in N2. J. Chem. Phys. 151, 114308 (2019)