NaI revisited: Theoretical investigation of predissociation via ultrafast XUV transient absorption spectroscopy

Abstract

Avoided crossings can trigger abrupt changes of electronic character and redirect the outcomes of photochemical reactions. Here, we report a theoretical investigation into core-level spectroscopic probing of predissociation dynamics of sodium iodide (NaI), a prototype system for studies of avoided-crossing dynamics. The elegant femtochemistry work of Zewail and co-workers pioneered the real-time dynamics of NaI, detecting the Na atoms bursting forth from the avoided crossing and the residual NaI molecules oscillating inside the quasi-bound potential. The simulated results show that core-level spectroscopy not only observes these integrated outcomes, but also provides a direct measure of the abrupt switching of electronic character at the avoided crossing. The valence and core-excited electronic structures of NaI are computed by spin-orbit general multi-configurational quasi-degenerate perturbation theory, from which core-level absorption spectra of the predissociation dynamics are constructed. The wave-packet motion on the covalent potential is continuously mapped as shifts in the absorption energies, and the switching between the covalent and ionic character at the avoided crossing is characterized as the sharp rise and fall of the Na + signal. The Na + signal is found to be insensitive to the wave-packet motion in the asymptotic part of the ionic potential, which in turn enables a direct measure of the nonadiabatic crossing probability excluding the effect of wave-packet broadening.

Reinvented: An Attosecond Chemist

“…Yuki Kobayashi and Kristina Chang pioneered major new attosecond chemical dynamics processes relating to curve crossings, conical intersections, and coherences (18,(68)(69)(70)(71). The theories set forth by Yuki Kobayashi, together with collaborator Professor Toby Zeng, are remarkable illustrations of how to interpret attosecond transient absorption chemical dynamics measurements (68,72). Joshua Vura-Weis and Chang-Ming Jiang succeeded in the first extreme ultraviolet solidstate charge transfer measurements, building a whole new apparatus in the process (73).…”

Attosecond Probing of Nuclear Vibrations in the D2+ and HeH+ Molecular Ions

“…Numerous other time-resolved imaging techniques have been developed over the past decades to monitor dynamical processes in molecules. These include laser Coulomb explosion imaging, − time-resolved X-ray scattering, , photoelectron holography, , transient absorption spectroscopy, , high-order-harmonic generation, , or multidimensional-quantum-beat spectroscopy. , Tracing of the femtosecond-coupled nuclear-electronic dynamics in a molecule was also considered on the basis of the characteristic harmonic generation emitted during the nonadiabatic transition. , …”

Tracing the vibrational dynamics of sodium iodide via the spectrum of emitted photofragments

“…time-resolved X-ray diffraction 8,9 or XUV-IR pump-probe scheme 10 to investigate molecular motion. Other imaging techniques like photoelectron holography, 11,12 laser Coulomb explosion imaging, [13][14][15] transient absorption spectroscopy [16][17][18] or multidimensional-quantum-beat spectroscopy 19,20 have been developed and applied with success to resolve the nuclear dynamics of small molecules. To observe wave packet dynamics in simple molecules, conventional pump-probe measurements are commonly applied in which the neutral H 2 /D 2 systems are ionized to create a vibrational wave packet in the H 2 + /D 2 + ions.…”