Hydrogen pairing

Figure 11-4. Mechanism of oxidation and reduction of nicotinamide coenzymes. There is stereospecificity about position 4 of nicotinamide when it is reduced by a substrate AHj. One of the hydrogen atoms is removed from the substrate as a hydrogen nucleus with two electrons (hydride ion, H ) and is transferred to the 4 position, where it may be attached in either the A or the B position according to the specificity determined by the particular dehydrogenase catalyzing the reaction. The remaining hydrogen of the hydrogen pair removed from the substrate remains free as a hydrogen ion.

Hodoshima, S., H. Arai, S. Takaiwa, and Y. Saito, Catalytic decalin dehydrogenation/ naphthalene hydrogenation pair as a hydrogen source for fuel-cell vehicle. Int. J. Hydrogen Energy., 28(11), 1255-1262 (2003). 

Ionic hydrogenation reactions85 involve the use of a hydrogenating pair consisting of a proton donor and a hydride ion donor. The ionic hydrogenation is based on the principle that the carbenium ion formed by the protonation of the double bond abstracts a hydride ion from the hydride source. 

Spohr provides a detailed discussion of the water pair correlation function at the water/Pt(100) interface." His results are shown in Fig. 3 for the oxygen-oxygen, oxygen-hydrogen and hydrogen-hydrogen pair correlations when one of the reference atoms is in either the first or the second layer, but otherwise a complete averaging over the locations and orientations of the other atom has been performed. The pair correlations... 

Several attempts were made, including attempts to correlate the IPs with the net charge of the electron-richest C atom of each molecule or with a combination of the electron-richest carbon-hydrogen pair of each molecule, all of which failed in giving any monotonic dependence of the IPs on these quantities. The only solution is that resulting from comparisons of ionization potentials with the electron-richest pair of bonded C atoms in each molecule. This correlation turns out to be linear (Fig. 7.1), although such a linearity had not been postulated a priori. The least-square... 

We will mainly be concerned with two- and three-body atomic and molecular systems whose components preserve their identity during the radiative encounters. In other words, we will consider non-reactive atomic or molecular systems, such as interacting helium and argon atoms, He-Ar, or hydrogen pairs, H2-H2, in their electronic ground states. 

Spectral moments can also be computed from classical expressions with Wigner-Kirkwood quantum corrections [177, 189, 317] of the order lV(H2). For the quadrupole-induced 0223 and 2023 components of H2-H2, at the temperature of 40 K, such results differ from the exact zeroth, first and second moments by -10%, -10%, and +30% respectively. For the leading overlap-induced 0221 and 2021 components, we get similarly +14%, +12%, and -56%. These numbers illustrate the significance of a quantum treatment of the hydrogen pair at low temperatures. At room temperature, the semiclassical and quantum moments of low order differ by a few percent at most. Quantum calculations of higher-order moments differ, however, more strongly from their classical counterparts. 

Fig. 6.3. The significant free —> free components of the spectral functions of molecular hydrogen pairs at 77 K. For a given set of expansion parameters A1A2AL, a different line type is chosen. When two curves of the same type are shown, the upper one represents the free — free, the lower the bound —< free contributions their sum is the total FG al T). The extreme low-frequency portion of the bound — free contributions with the dimer fine structures is here suppressed [282],...

Fig. 6.5. Computed structures due to the hydrogen dimer, in the quadrupole-induced (0223,2023) components near the So(0) line center at 120 K (the temperature of Jupiter s upper atmosphere). Superimposed with the smooth free — free continuum (dashes) are structures arising from bound — free (below 354 cm-1) and free - bound (above 354 cm-1) transitions of the hydrogen pair (dotted). The convolution of the spectrum with a 4.3 cm-1 slit function (approximating the instrumental profile of the Voyager infrared spectrometer) is also shown (heavy line) [282].

We note that a computational study of the dimer features is involved. It must account for the anisotropy of the interaction as this was done for the pure rotational bands of hydrogen pairs [355, 357], Whereas a treatment based on the isotropic potential approximation may be expected to predict nearly correct total intensities of the free-bound, bound-free, and bound-bound transitions involving the (H2)2 van der Waals molecule (and, of course, the free-free transitions which make up more than 90% of the observed intensities), the anisotropy of the interaction causes elaborate fine structure that is of considerable interest for the measurement of the anisotropy [248]. 

Recent reviews [342] suggest that the effect of molecular vibrations has not been studied in the rotovibrational collision-induced absorption spectra of H2 pairs, presumably due to the previous lack of a reliable interaction potential. Such data for hydrogen pairs do now exist and the influence of molecular vibrations on the collision-induced absorption spectra has recently been studied. Similar work on the H2-He system indicated significant effects of vibration on the spectral moments and the symmetry of the lines [151, 295, 294],... 

Previous work of the kind was generally based on empirical induced dipole models whose parameters were adjusted to fit measured spectra. For molecular systems like hydrogen pairs, empirical dipole models are highly simplified, for example, by either suppressing the anisotropic overlap terms, the AL = 21 components, in favor of an overlap term in the... 

J. Borysow, L. Trafton, L. Frommhold, and G. Birnbaum. Modelling of pressure-induced far infrared absorption spectra Molecular hydrogen pairs. Astrophys. J., 296 644, 1985. 

A.K. Soper and R.N. Silver, Hydrogen-hydrogen pair correlation function in liquid water, Phys. Rev. Lett., 49 (1982) 471-474. 

M. S. Brown and L. Frommhold. Dimer features in the translational depolarized Raman spectra of molecular hydrogen pairs. Chem. Phys. Lett., 127 191-199 (1986). 

In termisine, where the quinolizidine nucleus has a cis junction, the middle ring adopts a boat-like conformation illustrating the importance of the interaction of the H-8o/H-12P, H12-p/H-17p and H-14p/H-17p hydrogen pairs in sparteine and its derivatives. 

The semiconductor layers grown by the metal-organic vapour-phase epitaxy (MOVPE) generally contain hydrogen pairs or complexes originat-... 

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