Collisional deactivation

Miller L A and Barker J R 1996 Collisional deactivation of highly vibrationally excited pyrazine J. Chem. Phys. 105 1383-91... 

Hippier H, Troe J and Wendelken H J 1983 Collisional deactivation of vibrationally highly excited polyatomic molecules. II. Direct observations for excited toluene J. Chem. Phys. 78 6709... 

Pibel C D, Sirota E, Brenner J and Dai H L 1998 Nanosecond time-resolved FTIR emission spectroscopy monitoring the energy distribution of highly vibrationally excited molecules during collisional deactivation J. Chem. Phys. 108 1297-300... 

The chemical-activation step is between one and two orders of magnitude faster than the subsequent collisional deactivation of vibrationally excited O2. Finally, the population of individual vibrational levels v" of O2 is probed tluough LIF in the Schiunann-Runge band Oi X E") after exciting the oxygen... 

Figure B2.5.19. The collisional deactivation rate constant /c, (O3) (equation B2.5.42 ) as a fimction of the vibrational level v". Adapted from [ ]. Experimental data are represented by full circles with error bars. The broken curve is to serve as a guide to the eye.

Michaels C A, Mullin A S, Park J, Chou J Z and Flynn G W 1998 The collisional deactivation of highly vibrationally excited pyrazine by a bath of carbon dioxide excitation of the infrared inactive (10°0), (02°0), and (02 0) bath vibrational modes J. Chem. Phys. 108 2744-55... 

The 3 Pi/2, 3 P2/2 excited states involved in the sodium D lines are the lowest energy excited states of the atom. Consequently, in a discharge in the vapour at a pressure that is sufficiently high for collisional deactivation of excited states to occur readily, a majority of atoms find themselves in these states before emission of radiation has taken place. Therefore... 

Collisional Deactivation of (CwH2w ) + by Xenon. The excited C4H8+, formed by addition of C2H4+ to ethylene, if it is not deactivated. 

Flash photolysis studies<22) have indicated singlet methylene to be produced from the diazomethane-excited singlet upon loss of nitrogen followed by collisional deactivation to the triplet, the ground state multiplicity for this molecule. 

Gas-phase photolysis of diazoethane results in mixtures of ethylene, acetylene, and cis- and frans-2-butene. A mechanism involving the initial formation of ethylidene followed by formation of activated ethylene [which is collisionally deactivated or decomposes to produce acetylene and hydrogen— Eqs. (11.26(b,c,d)] or alternate attack on diazoethane to produce 2-butene [Eq. 11.26(e)] is proposed ... 

The efficiency of these radiative processes often increase at low temperatures or in solvents of high viscosity. Consequently emission spectra are generally run in a low-temperature matrix (glass) or in a rigid polymer at room temperature. The variation in efficiency of these processes as a function of temperature and viscosity of the medium indicates that collisional processes compete with radiative and unimolecular nonradiative processes for deactivation of the lowest singlet and triplet states. 

A singlet carbene was proposed to account for this stereoselectivity. Attempts to produce triplet carbene by collisional deactivation with octafluorocyclo-butane were unsuccessful and stereospecific addition to olefin still occurred. However, nonstereospecific addition to olefins and larger amounts of olefinic (insertion) products result from irradiation of the phenyldiazomethane in a frozen m-butene matrix at — 196°C ... 

Several mechanisms have been postulated in order to account for ketone-sensitized photodehydrochlorination. Benzophenone and acetophenone have been suggested to act as singlet sensitizers via a collisional deactivation process (13). An alternative mechanism proposed for benzophenone involves abstraction of a methylene hydrogen from PVC by the triplet ketone (Equation 2), followed by 3 scission of a... 

The acetone-sensitized photodehydrochlorination of 1,4-dichlorobutane is not suppressed by triplet quenchers (20), but the fluorescence of the sensitizer is quenched by the alkyl chloride (13). These observations imply the operation of a mechanism involving collisional deactivation, by the substrate, of the acetone excited singlet state (13,21). This type of mechanism has received strong support from another study in which the fluorescence of acetone and 2-butanone was found to be quenched by several alkyl and benzyl chlorides (24). The detailed mechanism for alkanone sensitization proposed on the basis of the latter work invokes a charge-transfer (singlet ketone)-substrate exciplex (24) and is similar to one of the mechanisms that has been suggested (15) for sensitization by ketone triplets (cf. Equations 4 and 5). 

However, as the pressure is decreased, one eventually reaches a point where the rate of the decomposition reaction becomes much larger than the collisional deactivation process, so that /c3 /c2[A]. In this situation the overall rate expression becomes second-order in A. 

Energy levels within an atom or molecule can be populated in several ways to produce more target species in the higher energy excited state than in the ground state. The population can occur by collisional processes such as between molecules in the interstellar medium and a balance can occur between the excitation process and a number of deactivation processes (Figure 3.17a). The population of level 2 can be subjected to ... 

Collisional deactivation. Collisions with other molecules can stimulate the relaxation to the ground state. There are no selection rules for collisionally induced transitions. 

Figure 1 Jablonski diagram showing energy levels and transitions F, fluorescence C, chemiluminescence P, phosphorescence CD, collisional deactivation IC, internal conversion ISC, intersystem crossing S0, ground singlet state S1( S2, excited singlet states Tl5 excited triplet state.

Flash photolysis experiments95, 97 have revealed the presence of S2(3E ) iQ its ground vibrational state. There is good reason to believe, however, that the product of reaction between S(1D2) and COS is S2(XA9) or S2(XS4) which is collisionally deactivated slowly to the ground state. Vibrational relaxation in the 3E state is very rapid. S2(3 ) disappears in a second-order reaction, presumably... 

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