Dissociation thresholds

Polik W F, Guyer D R and Moore C B 1990 Stark level-crossing spectroscopy of Sq formaldehyde eigenstates at the dissociation threshold J. Chem. Phys. 92 3453-70... 

At low energies the abstraction process dominates and at higher energies the exchange mechanism becomes more important. The cross-sections for the two processes crossing at 10 eV. The END calculations yield absolute cross-sections that show the same trend as the experimentally determined relative cross-sections for the two processes. The theory predicts that a substantial fraction of the abstraction product NHjD, which are excited above the dissociation threshold for an N—H bond actually dissociates to NH2D" + H or NH3 during the almost 50-ps travel from the collision chamber to the detector, and thus affects the measured relative cross-sections of the two processes. 

Similar calculations with consideration of the GP effect have also been reported [12]. A total of 24, 24, and 50 levels of Aj, A2, and E symmetries have been found below tbe dissociation threshold of the lower surface, —1.0560 eV. These are therefore genuine bound states the cone states lying above sucb a dissociation threshold are pseudobound states. The lowest levels of A, A2, and E symmetries are found to lie at —1.3475, —1.3438, and —1.3989eV, respectively. The notable feature is that the energy levels have been shifted due to the... 

By contrast, the dissociation channel leading to H + HCO (the radical channel) has no barrier and a dissociation threshold [49] of 30,328.5 cm. In 1993, van Zee et al. [50] found that excitation above this threshold led to CO rotational distributions that were bimodal. In addihon to the high-/ CO... 

Butler and co-workers have taken a unique approach to study the unimolecular dissociation of the vibrationally and rotationally hot allyl radical.150-152 They have examined the secondary C-H dissociation of the allyl radicals that are produced with high internal energies above the allyl dissociation thresholds in the primary photodissociation of allyl chloride and allyl iodide at 193 nm. The production of allene versus propyne (both at mass 40) from the secondary dissociation of the hot allyl radicals are... 

Next, we discuss the J = 0 calculations of bound and pseudobound vibrational states reported elsewhere [12] for Li3 in its first-excited electronic doublet state. A total of 1944 (1675), 1787 (1732), and 2349 (2387) vibrational states of A, Ai, and E symmetries have been computed without (with) consideration of the GP effect up to the Li2(63 X)u) +Li dissociation threshold of 0.0422 eV. Figure 9 shows the energy levels that have been calculated without consideration of the GP effect up to the dissociation threshold of the lower surface, 1.0560eV, in a total of 41, 16, and 51 levels of A], A2, and E symmetries. Note that they are genuine bound states. On the other hand, the cone states above the dissociation energy of the lower surface are embedded in a continuum, and hence appear as resonances in scattering experiments or long-lived complexes in unimolecular decay experiments. They are therefore pseudobound states or resonance states if the full two-state nonadiabatic problem is considered. The lowest levels of A, A2, and E symmetries lie at —1.4282,... 

The Vibrational Energies of Ozone up to the Dissociation Threshold Dynamics Calculations on an Accurate Potential Energy Surface. 

This is a Dunham-like expansion but done around the anharmonic solution. It converges very quickly to the exact solution if the potential is not too different from that of a Morse oscillator (Figure 2.3). This will not, however, be the case for the highest-lying vibrational states just below the dissociation threshold. The inverse power dependence of the potential suggests that fractional powers of n must be included (LeRoy and Bernstein, 1970). 

Table 19 reports multicollisional dissociation thresholds of the selected complexes. A direct correlation exists between them and the proton affinity (PA) of the guest. However, although chiral specificity has been observed in similar systems using ligand-exchange reactions (see previous sections), the results of Table 19 show no such specificity. The differences in binding of the Ala and Phe enantiomers are evidently too small to be measured with this method. 

Unfortunately, as with all oversimplified theories, there are limitations for the application of the latter equation to ions close to the dissociation threshold, hi these cases, the number of degrees of freedom has to be replaced by an effective number of oscillators which is obtained by use of an arbitrary correction factor. [7] However, as long as we are dealing with ions having internal energies considerably above the dissociation threshold, i.e., where E - Eo)/E = 1, the relationship is valid and can even be simplified to give the quasi-exponential expression... 

Reactions within and between partners may occur below the dissociation thresholds for simple dissociations. 

An ion formed with an internal energy higher than the dissociation threshold but with a sufficient lifetime that it can exit the source and enter the mass spectrometer where it dissociates... 

Figure 5. Series of IR femtosecond/picosecond laser pulses for the sequence of transitions OH(u = 10)- OH(u = 15) - 0 + H for the isolated model OH cf. Fig. 1 and Table I. The notations are as in Fig. 3 populations Pwen(t) = Xoio Po( ) and PCOnt(t) = lPweiKO indicate the total populations of bound and continuum states embedded in the potential well and above the dissociation threshold, respectively. The resulting spectrum of ATD is shown in Fig. 1.

Resonances in open systems, that is, systems whose total energy is higher than the first dissociation threshold, are an old theme of scattering dynamics. For very elementary introductions the reader is referred to, for example, Messiah (Ref. 1, Chapter HI), Cohen-Tannoudji et al. (Ref. 2, Chapter Xffl), Satchler (Ref. 3, Chapter 4), and Schinke (Ref. 4, Chapter 7). TTiey... 

The coupling between the angle y and the dissociation coordinate R is always large if Jacobi coordinates are used. At low energies deep inside the well, this coupling is linear and normal coordinates are usually better suited for interpretation and assignment than are Jacobi coordinates. However, if the molecular dynamics above the dissociation threshold is studied, the normal-mode picture breaks down and scattering coordinates have to be employed. 

D. M. Neumark In Lineberger s photoelectron spectrum of the HCO" ion, resonances above the H + CO dissociation threshold were observed. Were any resonances seen in this experiment that were not seen (at higher resolution) in the stimulated emission pumping work ... 

Figure 31. Variation of collision-induced dissociation thresholds (in center-of-mass system) for reactions indicated as function of source pressure.1080...

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