vibrostate

Vibrostate is a term used in physics and chemistry to denote the vibrational state of a system, typically referring to quantized vibrational modes of molecules or crystal lattices. In molecular systems, nuclei move in well-defined normal modes, each with its own frequency. The vibrostate of a molecule is the vibrational eigenstate described by a set of quantum numbers corresponding to the occupation of these modes. Transitions between vibrostates give rise to infrared and Raman spectra and are governed by selection rules that depend on the molecular symmetry and the harmonic or anharmonic character of the potential.

In condensed matter physics, lattice vibrations are quantized as phonons. A vibrostate in this context can refer to a particular occupation of phonon modes, or to a composite vibronic state in systems with significant electron–phonon coupling, where electronic states are dressed by vibrational excitations. The vibrational Hamiltonian for a system of normal modes is often written as H_vib = sum_k ħω_k (a_k† a_k + 1/2), with eigenstates labeled by mode occupations and energy given by E = sum_k ħω_k (n_k + 1/2).

Applications and study methods include vibrational spectroscopy, where vibrostates determine spectral lines, and computational approaches such as normal mode analysis, vibrational self-consistent field methods, quantum chemistry calculations, and density functional theory to predict vibrostate energies and transition intensities.

See also: phonon, vibrational spectroscopy, vibronic coupling, polaron.