Nonadiabatic electron wavepacket states in excited small carbon clusters

We report a new class of electronic excited states in small carbon clusters, which are found in the manifolds composed of many highly quasi-degenerate electronic excited states. In these manifolds, virtually any one of the highly excited adiabatic states undergoes frequent, intense, and continual multidimensional nonadiabatic transitions from many-states to many-states simultaneously. Consequently, dynamical nonadiabatic electron wavepackets make the most critical sense as a physical substance. We refer to these excited states as the complex electronic excited states. These states were first found in small boron clusters. The characteristics of the complex electronic excited states are: (1) the electron wavepacket propagates in time like a diffusion in the Hilbert space with a huge state fluctuation, (2) the electron dynamics is quantum-chaotic, (3) despite the huge electronic fluctuation, they are supported by rather strong chemical bonds, (4) the excess nuclear kinetic energy is dissipated to the electronic sea towards "equilibration" due to a "friction" induced by the continual nonadiabatic couplings and (5) despite the high electronic state energy, the clusters bear long-life times against molecular dissociation and ionization, and so on. In addition to the previously established analyses, we here perform the numerical analyses of the geometrical decomposition (collective coordinate analysis) of the nonadiabatic interactions [K. Takatsuka, <i>J. Chem. Phys.</i>, 2024, <b>160</b>, 044112] to quantify the concept of nonadiabatic burst and identify the origin of nonadiabatic chaos. We also propose an ionization profile from energy natural orbitals (ENOs) and its dynamics. Sonification of the dynamics of ENOs is also presented.