Vibrational energy relaxation
Encyclopedia
Vibrational energy relaxation, or vibrational population relaxation, is a process in which the population distribution of molecule
s in quantum states of high energy level
caused by an external perturbation returns to the Maxwell-Boltzmann distribution.
In solution
, the process proceeds with intra- and intermolecular energy
transfer. The excess energy of the excited vibrational mode is transferred to the kinetic modes in the same molecule or to the surrounding molecules. Through this process, the initially excited vibrational mode moves to a vibrational state of a lower energy. The relaxation is called the longitudinal relaxation, and the time constant of the relaxation is called the longitudinal relaxation time, or T1.
Vibrational energy relaxation has been studied with time-resolved spectroscopy
. By the excitation of the pump pulse, the population distribution of the vibrationally excited state is made by infrared absorption
or a Raman process
when the molecule is in the electronic ground state
. In addition, by the electronic transition, the molecule often moves to the vibrationally excited state of the electronic excited state. The process of the energy relaxation from these vibrationally excited states can be observed with the probe pulse, which is delayed from the pump pulse.
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s in quantum states of high energy level
Energy level
A quantum mechanical system or particle that is bound -- that is, confined spatially—can only take on certain discrete values of energy. This contrasts with classical particles, which can have any energy. These discrete values are called energy levels...
caused by an external perturbation returns to the Maxwell-Boltzmann distribution.
In solution
Solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
, the process proceeds with intra- and intermolecular energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
transfer. The excess energy of the excited vibrational mode is transferred to the kinetic modes in the same molecule or to the surrounding molecules. Through this process, the initially excited vibrational mode moves to a vibrational state of a lower energy. The relaxation is called the longitudinal relaxation, and the time constant of the relaxation is called the longitudinal relaxation time, or T1.
Vibrational energy relaxation has been studied with time-resolved spectroscopy
Time-resolved spectroscopy
In physics and physical chemistry, time-resolved spectroscopy is the study of dynamic processes in materials or chemical compounds by means of spectroscopic techniques. Most often, processes are studied that occur after illumination of a material, but in principle, the technique can be applied to...
. By the excitation of the pump pulse, the population distribution of the vibrationally excited state is made by infrared absorption
Infrared spectroscopy
Infrared spectroscopy is the spectroscopy that deals with the infrared region of the electromagnetic spectrum, that is light with a longer wavelength and lower frequency than visible light. It covers a range of techniques, mostly based on absorption spectroscopy. As with all spectroscopic...
or a Raman process
Raman spectroscopy
Raman spectroscopy is a spectroscopic technique used to study vibrational, rotational, and other low-frequency modes in a system.It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range...
when the molecule is in the electronic ground state
Ground state
The ground state of a quantum mechanical system is its lowest-energy state; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state...
. In addition, by the electronic transition, the molecule often moves to the vibrationally excited state of the electronic excited state. The process of the energy relaxation from these vibrationally excited states can be observed with the probe pulse, which is delayed from the pump pulse.