Striking Generic Impact of Light-Induced Non-Adiabaticity in Polyatomic Molecules

Abstract

Nonadiabaticity, i.e., the effect of mixing electronic states by nuclear motion, is a central phenomenon in molecular science. The strongest nonadiabatic effects arise due to the presence of conical intersections of electronic energy surfaces. These intersections are abundant in polyatomic molecules. Laser light can induce in a controlled manner new conical intersections, called light-induced conical intersections, which lead to strong nonadiabatic effects similar to those of the natural conical intersections. These effects are, however, controllable and may even compete with those of the natural intersections. In this work we show that the standard low-energy vibrational spectrum of the electronic ground state can change dramatically by inducing nonadiabaticity via a light-induced conical intersection. This generic effect is demonstrated for an explicit example by full-dimensional high-level quantum calculations using a pump-probe scheme with a moderate-intensity pump laser and a weak probe laser.

Born–Oppenheimer approximation in optical cavities: from success to breakdown

“…Our showcase example is the four-atomic H 2 CO (formaldehyde) molecule which has been investigated very recently for nonadiabatic phenomena induced by classical light. 26 This molecule does not exhibit any inherent nonadiabatic effects in the studied region of the nuclear conguration space (see further explanation in ESI †). Therefore, nonadiabatic effects appearing in the absorption spectrum of H 2 CO coupled to a single cavity mode can be attributed solely to the quantum LICI.…”

“…Moreover, LICIs are ubiquitous and become multidimensional in the nuclear coordinate space in polyatomic molecules due to the presence of several vibrational dofs. 25,26 Recently, efforts have been made to study light-induced nonadiabatic phenomena in optical or microwave cavities. [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] It has been successfully demonstrated that describing the photon-matter interaction with the tools of cavity quantum electrodynamics (cQED) [47][48][49][50] can provide an alternative way to study the quantum control of molecules with light.…”

“…[27][28][29]34,35,42 As is already clear from classical light, quantum LICI situations can also only occur if, in addition to the only vibrational dof, the rotational angle between the molecular axis and the polarization vector of the electric eld in the cavity is also accounted for (in case of diatomics) 37,38 or at least two vibrational dofs are considered in the description. 26,44 Furthermore, quantum light-induced collective nonadiabatic phenomena (collective LICI) can also emerge when many molecules are involved in strong coupling to the cavity mode. 34,35,42 Our current aim is to study pure quantum light-induced nonadiabatic phenomena in a single polyatomic molecule placed in an optical nanocavity with methods ranging from a full-dimensional and accurate quantum-dynamical description to a simple one-dimensional treatment.…”

Circularly polarized light-induced potentials and the demise of excited states

“…Then the coupling is zero and the molecule dissociates, while some population may be transferred to the ground potential by non-adiabatic processes in the vicinity of θ = π/2. In the representation of the LIPs, this process can be seen as fast internal conversion through a light-induced conical intersection 35–41 or LICI, using the language of Photochemistry, and it is possible even in diatomic molecules, including the rotational degree of freedom. There have been a plethora of studies concerning how to probe the LICIs and how to use them as a resource to control photochemical or photophysical processes, but if anything, one expects that the presence of LICIs will make it harder to stabilize the excited states of single electron molecules.…”

Quantum light-induced nonadiabatic phenomena in the absorption spectrum of formaldehyde: Full- and reduced-dimensionality studies

“…In contrast to natural CIs in field-free polyatomic molecules, the energetic and spatial position of LICIs can be controlled by varying the parameters of the laser field or cavity. The former case (classical laser light) has already been discussed several times, mainly in diatomics, [24][25][26][27] but in some situations in polyatomic molecules [28][29][30] as well, both theoretically [24][25][26][27][28][29][30] and experimentally. [31][32][33] However, the literature on the merits of the latter area…”