Single-step excitation

In the cascade decay of a laser-excited state, lower-lying states are populated as illustrated in the figure for the case of alkali atoms. This provides further possibilities for laser spectroscopy investigations. 

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Single-Step Excitation. Atoms are transferred directly from the ground state to the excited state using an allowed electric dipole transition. ThLs means an S-P transition for an alkali atom. 

Generation of (excited state) singlet S in the presence of parafHns yields the corresponding mercaptan by a concerted single-step insertion ... 

A concerted reaction is a chemical reaction in which all bond breaking and bond formation occurs in a single step in which reactive intermediates are not involved. Concerted photoreactions tend to be stereospecific, occurring from the vertical excited state. 

An exciting addition to the armoury of asymmetric phase transfer catalysed reactions has been the oxidative cyclisation of 1,5-dienes (Scheme 13) [21]. This tandem reaction process leads to the formation of tetrahydrofurans such as 35 in a single step from the open chain dienes 34. The step which determines the sense of asymmetry is the initial attack of permanganate anion, and this chiral information is efficiently relayed in the cyclisation to give products with three new stereogenic centres. For example, oxidation of the di-enone 34 with potassium permanganate, catalysed by the salt 36, gave the tetrahydrofuran 35 in 72% ee. 

By contrast, the alternative PCM-LR approach [15-17] determines in a single step calculation the excitation energies for a whole manifold of excited states. This general theory may be combined with the Time-Dependent Density Functional Theory (TDDFT) as QM level for the solute. Within the PCM-TDDFT formalism, the excitation energies are obtained by proper diagonalization of the free energy functional Hessian. 

Visible emissions can also be obtained by means of 2-step excited state absorption (ESA) mechanisms involving two different wavelengths [53,54] and a single ion. Pr3+ ions are first excited into the G4 level with 1010 nm light and then a second pump... 

A single-step electron transfer process between an excited molecule and ground-state molecule separated by a variable number of base pairs, DNA-mediated electron transfer. The possible occurrence of wire-like behavior in DNA has generated considerable controversy and the attention of the popular science press [16]. 

It has been suggested that in the solid state electronic energy migrates rapidly from the initially excited chromophore to excimer tr sites by either exciton diffusion or single-step mechanisms. 

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