Electronically excited atoms

Figure 7-11 and its caption (Crutzen, 1983) depict the most important of the gas phase and photochemical reactions in the atmosphere. Perhaps the single most important interaction involves the hydroxyl free radical, OH-. This extremely reactive radical is produced principally from the reactions of electronically excited atomic oxygen, 0( D), with water vapor. Photo-... 

Preliminary activation may be performed not only by means of dissociation of the components being analyzed, but also by electronic and vibrational excitation, either in the gaseous phase, or even better, directly on the film of semiconductor sensor. It should be also noted that this method is applicable to dissociation in the adsorbed layer. Excitation of the molecules in adsorbed layer (we are referring to physically adsorbed particles) can be performed optically, by an electron (ion) beam, or by an electronically excited atom beam, by Hg, for example [10, 11]. 

A distinguishing feature of electronically excited atoms and molecules is that they have one or a few excited orbitals of an electron. The principal properties of these particles are represented by a high internal energy potential localized on the excited orbitals and the structure of electron shell essentially different from the electron ground state. 

Figure 1.14 Light amplification resulting from stimulated emission ( represents an electronically-excited atom)...

FIGURE 3.7 Potential energy curves for a hypothetical diatomic molecule showing electronic transitions to two repulsive excited states having no minima. A is an electronically excited atom. 

The production of an electronically excited atom following a metathetical reaction between a ground state atom and a diatomic molecule is a novel type of process and of theoretical interest.35 Polanyi et al.15,38 have studied this in detail for the reactions ... 

To observe the kinetic effect of the chemical reaction of an electronically excited atom, the rate must be significantly different from that of the ground state atom, as spin orbit relaxation may compete with reaction. The separation of these processes is inherent in studies of the reactions of excited halogen atoms. Clearly, where a strong attractive potential facilitates chemical reaction, this chemical interaction will also aid spin orbit relaxation itself (Section VII). Thus relatively strongly endothermic, slow, chemical reaction... 

The emission from electronically excited atomic and molecular oxygen is the cause of the night airglow. The atmospheric glow originates in the upper atmosphere where the pressure is so low that the radiative decay can compete favourably with the collisional deactivations. 

Collisions of Electronically Excited Atoms and Molecules (Muschlitz) 10 121... 

Production, detection, and reactivities of various electronically excited atoms arc given in Chapter IV. The importance of electronically excited atom reactions in photochemistry has been recognized only recently. 

Production and Quenching of Electronically Excited Atoms addition to 1-butene were found. The process... 

Electronically excited atoms have been known to play important roles in many photochemical reactions. 

In this chapter electronically excited atoms are classified into two groups. The lirst group of excited atoms are those that are formed by resonance absorption and decay rapidly by fluorescence if not quenched by collisions with foreign gases. Examples are electronically excited Hg, Cd, H, Ar, Kr, and Xe atoms. Of these Hg(,/>1) atoms and their reactions have been most extensively studied. The mercury sensitized reactions provide a convenient way to generate atoms and radicals in the spectral region where many molecules do not absorb. 

The second group of electronically excited atoms consists of metastable atoms such as O( D) and Of S). These metastable atoms cannot be produced directly from ground state atoms by light absorption. However, they are often formed in photodissociation of molecules. The production of metastable atoms from photodissociation has been known by the different reactivities of the metastables from those of corresponding ground state atoms. 

Electronically excited atoms produced by resonance absorption have a short life, on the order of 1 to 100 nsec, after which they return to the ground... 

Tables VI-3n and 3h shows that the photolysis above 1200 A can produce electronically excited atoms 0( D, 5) N(2/3,2P) and molecules N2(/t3Z, fl- fl). Of these 0( 5) and N2(B2n) are directly observed by the emission at...

COLLISIONAL ENERGY-TRANSFER SPECTROSCOPY WITH LASER-EXCITED ATOMS IN CROSSED ATOM BEAMS A NEW METHOD FOR INVESTIGATING THE QUENCHING OF ELECTRONICALLY EXCITED ATOMS BY MOLECULES... 

Substantial advances in the understanding of microscopic processes of electronically excited atoms began only in the 1960s, when improvements in experimental methods and available technology allowed scientists to obtain quantitative microscopic information under well-defined conditions. 

The branching ratio is 1 1000 in favor of the ground state. The beam is scattered from a second supersonic beam, and the electronically excited atoms are detected. As excitation transfer can occur during the collision (e.g., He + Ne— He + Ne ), a second quench lamp is sometimes installed in front of the detector, to enable study of the energy-transfer process separately. 

Asymptotically, one beam can be prepared to carry electronically excited atoms (A) and the other ground-state atoms (B), and thus the wave function can be written as... 

Collisional Energy-transfer Spectroscopy with Laser-excited Atoms in Crossed Atom Beams A New Method for Investigating the Quenching of Electronically Excited Atoms by Molecules... 

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