Internal energy transfer

Translational -> internal energy transfer Surface excitation (phonon, electron)... 

Here again there is evidence that vibrationally excited CH4 + can react with some kinetic to internal energy transfer and produce ions which... 

The internal energy transfer along the electric field is Qi (units erg s-1) given by... 

The amount of internal energy transferred to the precursor depends on the type of mass analyzer used, as well as user settings. The number of collisions occurring and the energy of these collisions as well as the mass of the neutral collision gas used affect the degree of fragmentation. 

Resonances are common and unique features of elastic and inelastic collisions, photodissociation, unimolecular decay, autoionization problems, and related topics. Their general behavior and formal description are rather universal and identical for nuclear, electronic, atomic, or molecular scattering. Truhlar (1984) contains many examples of resonances in various fields of atomic and molecular physics. Resonances are particularly interesting if more than one degree of freedom is involved they reflect the quasi-bound states of the Hamiltonian and reveal a great deal of information about the multi-dimensional PES, the internal energy transfer, and the decay mechanism. A quantitative analysis based on time-dependent perturbation theory follows in the next section. 

Fig. 7. (a) Scheme and one-dimensional potentials of internal energy transference path-... 

In the ion sources, the analysed samples are ionized prior to analysis in the mass spectrometer. A variety of ionization techniques are used for mass spectrometry. The most important considerations are the internal energy transferred during the ionization process and the physico-chemical properties of the analyte that can be ionized. Some ionization techniques are very energetic and cause extensive fragmentation. Other techniques are softer and only produce ions of the molecular species. Electron ionization, chemical ionization and field ionization are only suitable for gas-phase ionization and thus their use is limited to compounds sufficiently volatile and thermally stable. However, a large number of compounds are thermally labile or do not have sufficient vapour pressure. Molecules of these compounds must be directly extracted from the condensed to the gas phase. 

The kinetic energy for internal energy transfers is governed by the laws concerning collisions of a mobile species (the ion) and a static target (the collision gas). 

Figure 3.3 Complex relaxation process in which internal energy transfer occurs with relaxation time t12.

The deduction is based upon assuming that one of the oscillators is a weak bond which will break when energy E is present in it. For a molecule that consists of n weakly coupled harmonic oscillators the chance that, when the molecule has energy E, at least E of it will be localized in one oscillator is given by (1 — E /E) . The rate at which such an event happens, k E), is then presumed proportional to this ratio, the constant of proportionality being A, the mean rate of internal energy transfer in the molecule. This derivation may be justified for a classical and for a quantized molecule. 

When P(E) is not perturbed by the reaction, so that the distribution of critically energized molecules is that characteristic of equilibrium, the RRK model leads to a specific first-order rate constant of the form k = A exp —E /RT) where A is the frequency of internal energy transfer between oscillators. The Slater formulation in these circumstances gives k = V exp —E /RT ), both results being similar in form to the Arrhenius equation. The A factor in the RRK model represents the frequency of energy transfer between oscillators, which Jor weakly coupled oscillators would be of the order of their beat frequencies, or about 10 to 10 sec In the Slater model, V represents a weighted rms frequency of the normal frequencies which describe the decomposition [Eq. (X.6.1)]... 

Because of the difficulty of distinguishing the RRK and Slater models experimentally and the unsettled question of whether or not internal energy transfer may take place between loosely coupled oscillators, we... 

Use of an appropriate rare gas allows the control of the internal energy transferred to the ions formed, and fragmentation can be diminished or made more significant. By eliminating extensive fragmentation during ion formation, MAB can be used in connection with Py-MS. MAB can also be used in combination with MS/MS analysis of the pyrolysates. 

ENDOTHERMIC REACTION AND THE PROBLEM OF KINETIC-TO-INTERNAL ENERGY TRANSFER... 

In Equation 4, AEm is the average internal energy transferred from excited species A upon collision with M, which may be either nonreactive bath gas or reactant molecules, and ka(E ) is the RRKM rate constant for imimolecular decomposition calculated at each energy E. Eventually after successive energy degrading collisions without unimolecular decomposition the excited molecule may be stabilized to an energy level below the critical decomposition threshold Ec. 

Results of the treatment confirm that strong colliders like parent cyclobutane can transfer on the order of 10 kcal/mol per collision and that even monatomic weak colliders can transfer up to 3 or 4 kcal/mol on collision if they have suflBcient mass. A combined tabulation of results to date on absolute quanta of internal energy transferred from excited cyclobutane to various bath gases is given in Table I (6, JO). 

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