Field dissociation spectroscopy

N.J. Bjerre, S.R. Keiding, Long-range ion-atom interactions studied by field dissociation spectroscopy of molecular ions. Phys. Rev. Lett. 56, 1458 (1986)... 

The combination of fast ion beam photofragmentation with field-dissociation spectroscopy opens interesting new possibilities for studying long-range ion-atom interactions. This has been demonstrated by Bjerre and Keiding [9.83], who measured the 0 —O potential in the internuclear dis-... 

In low-dimensional systems, such as quantum-confined. semiconductors and conjugated polymers, the first step of optical absorption is the creation of bound electron-hole pairs, known as excitons [34). Charge photogcncration (CPG) occurs when excitons break into positive and negative carriers. This process is of essential importance both for the understanding of the fundamental physics of these materials and for applications in photovoltaic devices and photodctcctors. Since exciton dissociation can be affected by an external electric field, field-induced spectroscopy is a powerful tool for studying CPG. 

Accurate potential functions for chemically stable diatomic molecules are well known thanks to extensive studies in the field of spectroscopy. The potential in the vicinity of the equilibrium position of the (usually deep) well has been determined for both ground and excited molecular states. Such studies have also yielded information on repulsive parts of potential curves, especially when light absorption or emission leads to dissociation, as in Chapter 7. Other important sources have been the measured temperature dependence of the deviation from ideal gas behavior and of u-ansport coefficients, and from lattice energies and compressibility of solids. 

In addition to the natural improvements expected in the accuracy of the measurements, and the increased scope in the types of systems examined, new techniques go beyond the issue of thermochemistry to allow for very detailed studies of reaction dynamics. The investigation by Zewail and co-workers of the reactivity of planar COT" on the femtosecond time scale is likely only the beginning. Time-resolved photoelectron spectroscopy, for example, has recently been used to map the potential energy surfaces for the dissociation of simple ions IBr and l2. " Although applications in the field of organic reactive molecules are likely far off, they are now possible. 

The simplest and first observation of the excitation of molecules by strong laser fields was the identification with TOF spectroscopy of the following dissociation channel —> I2+ + I°+ [31]. In this example, a short laser... 

An additional complexity arises from the dissociation of water molecules which occurs when alkaline-earth-exchanged zeolites are thermally activated since several modes of dehydroxylation are possible. This problem has been extensively investigated by IR spectroscopy, in particular by Ward (268,269) and Uytterhoeven et ai (270), and by X ray (271). They concluded that the electrostatic field associated with the cation causes dissociation of adsorbed water to produce acidic hydroxyl groups. The dissociation reaction may occur according to the following reactions ... 

Field ionization mass spectroscopy of chemically reactive molecular gases found often dissociated species and associated species of these... 

Bandrauk s long-term research interests include the dressed-state representation of molecular spectroscopy. His contributions to the nonperturba-tive treatment of molecular spectroscopy from the weak field to strong field limits have been summarized in two chapters in a book he edited in 1993.286 Bandrauk and his coworkers published the first theoretical demonstration of the use of chirped pulses to effect laser bond breaking in less than a picosecond.287 His other firsts include the first prediction of molecular stabilization in intense laser fields288 and the first complete non-Born-Oppenheimer calculation of dissociative ionization of molecules in intense femtosecond laser pulses.289... 

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]...

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