Translational energy release data

The translational energy releases reported in the literature for metastable ion decompositions are contained in Tables 1—7. Decompositions of positive ions occurring within an ion source are covered in Table 8 and decompositions of negative ions in an ion source in Table 9. Translational energy releases determined by photoion—photoelectron coincidence (PIPECO) appear, therefore, in Table 8. The results from the extensive series of electron impact (El) measurements [310] at ionizing energies close to threshold appear in Tables 8 and 9. Coverage of dissociations of diatomic ions is not exhaustive. 

Coincidence techniques have been used to study both of the singly charged positive ions resulting from dissociation in the ion source of a doubly charged ion formed by El [125], The translational energy distributions of both product ions were determined with a number of diatomic molecules.  

The translational energies released in the decompositions of doubly charged metastable ions have been extensively investigated [6, 8—10, 33, 34, 66, 67, 69, 71, 75, 155, 192, 283, 385, 386, 606, 647, 651, 664, 701, 830, 874], Most of these doubly charged metastable ions have been formed by EL Field ionization has also been employed [617]. Triply charged metastable ions have also been reported [68, 450]. Doubly charged diatomic ions can have lifetimes of the order of microseconds [72, 650, 651]. 

Translational energy release accompanying loss of an atom from metastable ions (See Sect. 8.5.1 for explanation of symbols used.) 

Decomposing Neutral precursor Energy release Notes Ref. 

The translational energy releases reported in the literature for metastable ion decompositions are contained in Tables 1—7. Decompositions of positive ions occurring within an ion source are covered in Table 8 and decompositions of negative ions in an ion source in Table 9. Translational energy releases determined by photoion—photoelectron 

Decomposing ion Neutral precursor Energy release (meV) Notes Ref. 

---

In addition to CO(v = 0—2,7) populations, Houston and Kable recorded CO Doppler profiles to measure the translational energy release, and the vector correlation between the recoil velocity vector and the angular momentum vector of CO. Together, these data paint a compelling picture that two pathways to CH4 + CO are operative. The rotationally hot CO population (85% of total CO)... 

Theories of translational energy release in unimolecular decompositions are discussed in Sect. 8.1. Qualitative lines of explanation are discussed, in conjunction with the experimental results to which they relate, in Sects. 8.2—8.4. The extensive data on translational energy releases in source reactions, including PIPECO, and in metastable ion decompositions are collected together in tables (Sect. 8.5). The emphasis is on decompositions of polyatomic ions, although many triatomics are included in the tables. The coverage includes both fundamental and mechanistic studies. 

It has been mentioned that phase space theory, i.e. assuming a loose transition state, has been able to explain the translational energy releases in the decomposition of certain ion—molecule collision complexes [485] and in some unimolecular decompositions measured by PIPECO (see Sect. 8.2). There is a larger number of translational energy releases from PIPECO and a body of data as to translational energy releases in source reactions of positive ions formed by El [162, 310] (Sect. 8.3.1) with which the predictions of phase space theory are in poor agreement. The predicted energy releases are too low. 

Data from the laser-induced fluorescence of C2 radicals obtained in the laboratory during 193 nm photolysis of C2H2 have been used to explain band profiles of C2 in the nucleus of comet Hyakutake, observed by the Hubble Space Telescope. In conjunction with ab initio computations, the data have led to the proposal that photolysis of C2H2, in the laboratory and in comets, proceeds by a sequential mechanism, first producing C2H and then C2. Two excited electronic states of C2H have been identified and 2 11) through which photodissociation in the second step occurs. Measurements of the kinetics and translational energy release in the near-UV photodissociation of the allyl radical have indicated that allene formation is the dominant H-loss reaction channel. ... 

The masses used in calculating the velocity of the indicated fragment in Fig. 2 were 146 and 46 amu, which correspond to the pair of fragments produced in the primary dissociation of TNAZ. The velocity shown is for the heavier fragment and was calculated for the maximum translational energy released in the reaction. This information was obtained from the analysis of time-of-flight data collected, which will be discussed later. 

For RDX the distribution peaks at zero, but for TNAZ the peak near 5 kcal/mol. The RDX data may have been obscured in the low energy part of the secondary NOj loss due to the many other channels participating in the decomposition of this molecule. One may speculate that the secondary loss of NO2 in RDX ahio proceeds over a small barrier, which would explain the noticeably higher translational energy released in the second NOj loss step compared to the first. 

The rotational and the translational freedom appear after desorption of adsorbed molecules and each energy is kept without any disturbance before detection in the present experimental condition, since there is no collision and the lifetime of the excited states for a desorbed molecule is long. The experimental data can be analyzed by a simple model using the impulse scheme, con fi ned to the momentum transferred from the substrate to an adsorbate atom, in which the form of the excited-state PES and the transition process need not be assumed [68, 69]. The energy released from the excited state is converted to the momentum and this energy is transferred impulsively. The desorption also occurs impulsively. This simple model sheds hght on the property of the intermediate excited state, and the intermediate excited state plays an important role in the DIET process. 

---