Excimer

Summary

An excimer (originally short for excited dimer) is a short-lived dimeric or heterodimeric molecule formed from two species, at least one of which has a valence shell completely filled with electrons (for example, noble gases). In this case, formation of molecules is possible only if such atom is in an electronic excited state. Heteronuclear molecules and molecules that have more than two species are also called exciplex molecules (originally short for excited complex). Excimers are often diatomic and are composed of two atoms or molecules that would not bond if both were in the ground state. The lifetime of an excimer is very short, on the order of nanoseconds. Formation and decay Under the molecular orbital formalism, a typical ground-state molecule has electrons in the lowest possible energy levels. According to the Pauli principle, at most two electrons can occupy a given orbital, and if an orbital contains two electrons they must be in opposite spin states. The highest

Official source

https://en.wikipedia.org/wiki/Excimer

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Interaction of highly excited molecules with solid surfaces

Mathieu Schmid

EPFL2003

Collision-free infrared multiphoton dissociation of silane

Joachim Makowe, Thomas Rizzo

We have measured an upper limit of 17 J/cm(2) for the threshold fluence for collision-fret CO2 laser IRMPD of silane by detecting the SiH2 product in its electronic and vibrational ground state. The threshold drops to similar to4 J/cm(2) when silane molecules are irradiated by all lines from a pulsed NH3 laser. This value further drops to less than 2 J/cm(2) when the molecules are pre-excited to the first Si-H stretch overtone. Using the NH3 laser on the 868 cm(-1) line, the dissociation yield of pre-excited SiH4 reaches saturation at a laser fluence of 6 J/cm(2). The substantial difference in the fluence threshold and optimal dissociation frequency of the ground and excited molecules allows us to perform highly selective dissociation of pre-excited silane in the presence of a large excess of ground-state molecules.

2000

Dynamics of photoexcited Ba+ cations in 4He nanodroplets

Marcel Drabbels, Alberto Hernando de Castro, Xiaohang Zhang

We present a joint experimental and theoretical study on the desolvation of Ba+ cations in 4He nanodroplets excited via the 6p 6s transition. The experiments reveal an efficient desolvation process yielding mainly bare Ba+ cations and Ba+Hen exciplexes with n = 1 and 2. The speed distributions of the ions are well described by a Maxwell-Boltzmann distributions with temperatures ranging from 60 to 178 K depending on the excitation frequency and Ba+Hen exciplex size. These results have been analyzed by calculations based on a time-dependent density functional description for the helium droplet combined with classical dynamics for the Ba+. In agreement with experiment, the calculations reveal the dynamical formation of exciplexes following excitation of the Ba+ cation. In contrast to experimental observation, the calculations do not reveal desolvation of excited Ba+ cations or exciplexes, even when relaxation pathways to lower lying states are included.

American Institute of Physics2016