Carbon monoxide vibrational relaxation

The dynamics of fast processes such as electron and energy transfers and vibrational and electronic deexcitations can be probed by using short-pulsed lasers. The experimental developments that have made possible the direct probing of molecular dissociation steps and other ultrafast processes in real time (in the femtosecond time range) have, in a few cases, been extended to the study of surface phenomena. For instance, two-photon photoemission has been used to study the dynamics of electrons at interfaces [ ]. Vibrational relaxation times have also been measured for a number of modes such as the 0-Fl stretching m silica and the C-0 stretching in carbon monoxide adsorbed on transition metals [ ]. Pump-probe laser experiments such as these are difficult, but the field is still in its infancy, and much is expected in this direction m the near fiitiire. 

Margottin-Maclou M, Doyennette L and Henry L 1971 Relaxation of vibrational energy in carbon monoxide, hydrogen chloride, carbon dioxide and nitrous oxide App/. Opt. 10 1768-80... 

The lowest excited triplet states of a-dicarbonyl compounds are considerably less energetic than those of simple carbonyls. For instance the energy of the vibrationally relaxed triplet of glyoxal is 55 kcal,366 as compared to 72 kcal for formaldehyde. Irradiation of glyoxal at 4358 A populates the lowest vibrational levels of the first excited singlet, 30% of which fluoresce and 70% of which cross over to the triplet manifold.388 Almost all of the triplet molecules then decompose to formaldehyde and carbon monoxide, the phosphorescence yield being only 0.1%. 

Hill J R ef a/1995 Vibrational relaxation of carbon monoxide in model heme compounds 6-coordinate metalloporphyrins (M = Fe, Ru, Os) Chem. Phys. Lett. 224 218-23... 

Stretching motion (amide I mode) was found to occur on a 1 picosecond or subpicosecond timescale [24-28], whereas vibrational relaxation of photolyzed carbon monoxide in the heme pocket can last from tens to hundreds of picoseconds in different Mb mutants [7,29,30], Starting from a basis of harmonic normal modes and including the contribution of cubic anharmonicity in the potential energy, providing nonlinear coupling, Leitner and coworkers estimated the thermal diffusivity of Mb at 300K to be 14 ps", approximately the value for water. The thermal conductivity... 

Sagnella, D. E. Straub, J. E. Jackson, T. A. Lim, M. Anfinrud, P. A., Vibrational population relaxation of carbon monoxide in the heme pocket of photolyzed carhonmonoxy myoglobin Comparison of time-resolved mid-lR absorbance experiments and molecular dynamics simulations. Proc. Natl. Acad. Sci. U. S. A. 1999, 96, 14324—14329. 

Addition of singlet CDa (. 1), from the photolysis of CDa C 0, to the fluoro-olefins, Rp CF CFa (Rp = CF3, CFs CFa CFa, or CFs CFa CFa CFa CFa-) in the presence of carbon monoxide yields chemically activated cyclopropane, which may relax or expel difluorocarbene (see Scheme 4). At low pressures, ranging from <650 Torr for Rp = CFa down to <0.25 Torr for the more complex Rp = CsFii, the rate of cyclopropane decay is independent of pressure, but then it increases with increasing pressure. Relaxation of internal vibration energy is not instantaneous, the time required being longest when the vibrational modes available are fewest. ... 

Sagnella, D.E., Straub, J.E. A study of vibrational relaxation of B-state carbon monoxide in the heme pocket of photolyzed carboxymyoglobin. Biophys. J. 77, 70-84 (1999)... 

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