Hydrogen weakly bound species

It should be noted that (depending on the metal face, the coverage, and/ or the temperature) a given symbol can denote different surface species. For example, C2Hi(a) could denote a di-surface species is relevant has to be considered in each particular case. 

This vibrational cooling is sufficient to stabilize complexes that are weakly bound by van der Waals or hydrogen-bonding forces. The pure rotational spectra and structure of species such as... 

Second, catalytic reactions do not necessarily proceed via the most stable adsorbates. In the ethylene case, hydrogenation of the weakly bound Jt-C2H4 proceeds much faster than that of the more stable di-cr bonded C2H4. In fact, on many metals, ethylene dehydrogenates to the highly stable ethylidyne species, =C-CH3, bound to three metal atoms. This species dominates at low coverages, but is not reactive in hydrogenation. It is therefore sometimes referred to as a spectator species. Hence, weakly bound adsorbates may dominate in catalytic reactions, and to observe them experimentally in situ spectroscopy is necessary. 

Figures 2.a-c show the pyridine adsorption results. Bronsted acidity is manifested by the bands at 1440-1445,1630-1640 and 1530-1550 cm . Bands at 1600-1630 cm are assigned to pyridine bonded to Lewis acid sites. Certain bands such as the 1440-1460 and 1480-1490 cm can be due to hydrogen-bonded, protonated or Lewis-coordinated pyridine species. Under continuous nitrogen purging, spectra labeled as "A" in Figures 2a-c represent saturation of the surface at room temperature (90 25 unol pyridine/g found in all three tungsta catalysts) and "F" show the baseline due to the dry catalyst. We cannot entirely rule out the possibility of some extent of weakly bound pyridine at room temperature. Nevertheless, the pyridine DRIFTS experiments show the presence of Brpnsted acidity, which is expected to be the result of water of reduction that did not desorb upon purging at the reduction temperature. It is noted that, regardless of the presence of Pt, the intensity of the DRIFTS signals due to pyridine are...

We now turn to the addition of hydrogen to 3Fe(CO)3. This is hypothesized to be the process that leads to the short-lived species formed in sc Ar upon photolysis of iron pentacarbonyl in the presence of H2 (24). It is however possible that Fe(CO)3 is present instead in the form of the weakly bound 3Fe(CO)3(Ar) species under these conditions. However, the reaction has also been studied in the gas phase, where a room-temperature rate constant of 2.7 x 10 11cm3molecule 1s 1 was reported (49,55), again corresponding to a very large, near collision-limit value. 

A novel form of Y HX hydrogen bonding49 results when the Lewis base Y is itself a hydride ion (H-). Because the electron affinity of a hydrogen atom is extremely weak (21 kcal mol-1), the H- ion is among the most weakly bound and diffuse anionic species known, and hence a powerful Lewis base. In this case, the H - -HX complex can be referred to as a dihydrogen bond 50 to denote the unusual H-bonding between hydrogen atoms. A water complex of this type was... 

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