Spectroscopy of dissociating molecules

Imre, D., Kinsey, J. L., Sinha, A., and Krenos, J. (1984), Chemical Dynamics Studied by Emission Spectroscopy of Dissociating Molecules, J. Phys. Chem. 88, 3956. 

Imre, D., Kinsey, J.L., Sinha,. 4., and Krenos, J. (1984) Chemical dynamics studied by emission spectroscopy of dissociating molecules,. 7. Phys. Chem. 88, 3956-3964. Untcli, A., Weide, K., and Schinke, R. (1985) The direct photodissociation of ClNO(Si) An exact threc-dimeiisional wave packet analysis, J. Chem. Phys. 95. 6496-6507. 

Johnson B R, Kittrell C, Kelly P B and Kinsey J L 1996 Resonance Raman spectroscopy of dissociative polyatomic molecules J. Chem. Educ. 100 7743-64... 

Figure 24. Coincidence-imaging spectroscopy of dissociative multiphoton ionization processes in NO2 with 100-fs laser pulses at 375.3 nm, using angle-angle correlations. The polar plots show, at time delays of Ofs, 350 fs, 500 fs, 1 ps, and 10 ps, the angular correlation between the ejected electron and NO photofragment when the latter is ejected parallel to the laser field polarization vector. The intensity distributions change from a forward-backward asymmetric distribution at early times to a symmetric angular distribution at later times, yielding detailed information about the molecule as it dissociates. Taken with permission from Ref. [137]...

Bagratashvili, V. N., Ionov, S. L, and Makarov, G. N. (1989). Laser IR spectroscopy of polyatomic molecules near and above the dissociation limit. In Laser spectroscopy of highly vibrationally excited molecules (ed. V. S. Letokhov), pp. 265 328. Adam Hilger, Bristol. 

Time-of-flight mass spectrometers have been used as detectors in a wider variety of experiments tlian any other mass spectrometer. This is especially true of spectroscopic applications, many of which are discussed in this encyclopedia. Unlike the other instruments described in this chapter, the TOP mass spectrometer is usually used for one purpose, to acquire the mass spectrum of a compound. They caimot generally be used for the kinds of ion-molecule chemistry discussed in this chapter, or structural characterization experiments such as collision-induced dissociation. Plowever, they are easily used as detectors for spectroscopic applications such as multi-photoionization (for the spectroscopy of molecular excited states) [38], zero kinetic energy electron spectroscopy [39] (ZEKE, for the precise measurement of ionization energies) and comcidence measurements (such as photoelectron-photoion coincidence spectroscopy [40] for the measurement of ion fragmentation breakdown diagrams). 

The decomposition of tri- and tetrasulfane in CCI4 solution (0.2 mol 1 ) at 70 °C and in the absence of oxygen has been studied by H NMR spectroscopy [64]. Initially, tetrasulfane decomposes to a mixture of tri- and pentasul-fane but slowly and after an induction period hydrogen sulfide and disulfane are formed in addition. These results have been interpreted in terms of a radical-chain reaction. The initial step is assumed to be the homolytic cleavage of the central SS bond which has by far the lowest dissociation enthalpy of the molecule ... 

Figure 1.3. Real-time femtosecond spectroscopy of molecules can be described in terms of optical transitions excited by ultrafast laser pulses between potential energy curves which indicate how different energy states of a molecule vary with interatomic distances. The example shown here is for the dissociation of iodine bromide (IBr). An initial pump laser excites a vertical transition from the potential curve of the lowest (ground) electronic state Vg to an excited state Vj. The fragmentation of IBr to form I + Br is described by quantum theory in terms of a wavepacket which either oscillates between the extremes of or crosses over onto the steeply repulsive potential V[ leading to dissociation, as indicated by the two arrows. These motions are monitored in the time domain by simultaneous absorption of two probe-pulse photons which, in this case, ionise the dissociating molecule.

Figure 1.4. Experimental and theoretical femtosecond spectroscopy of IBr dissociation. Experimental ionisation signals as a function of pump-probe time delay for different pump wavelengths given in (a) and (b) show how the time required for decay of the initally excited molecule varies dramatically according to the initial vibrational energy that is deposited in the molecule by the pump laser. The calculated ionisation trace shown in (c) mimics the experimental result shown in (b).

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