Articles you may be interested inVibrational spectroscopy and relaxation of an anharmonic oscillator coupled to harmonic bath Picosecond infrared pump-probe experiments are used to measure the vibrational lifetime of the asymmetric (T 1u ) CO stretching mode of W͑CO͒ 6 in supercritical CO 2 , C 2 H 6 , and CHF 3 as a function of solvent density and temperature. As the density is increased at constant temperature from low, gaslike densities, the lifetimes become shorter. However, in all three solvents, it is found that within a few degrees of the critical temperature (T r ϵT/T c Ϸ1.01), the lifetimes are essentially constant over a wide range of densities around the critical value ( c ). When the density is increased well past c , the lifetimes shorten further. At higher temperature (T r ϭ1.06) this region of constant vibrational lifetime is absent. Infrared absorption spectra of W͑CO͒ 6 and Rh͑CO͒ 2 acac in supercritical CO 2 , C 2 H 6 , and CHF 3 acquired for the same isotherms show that the vibrational spectral peak shifts follow similar trends with density. The peak positions shift to lower energy as the density is increased. Near the critical point, the peak positions are density independent, and then redshift further at densities well above c . It is shown that critical fluctuations play a dominant role in the observed effects. Theoretical calculations ascribe the density independence of the observables to the cancellation of various rapidly changing quantities near the critical point. The theory's calculation of density independence implicitly involves averages over all local densities and does not involve any form of solute-solvent clustering.
Vibrational lifetime and spectral shift data for the asymmetric CO stretching mode of W(CO) 6 in supercritical ethane, carbon dioxide, and fluoroform as a function of density at two temperatures are presented, and the lifetime (T 1 ) measurements are compared to theory. The data and theory are refinements of previous work. Measurements at zero density allow the contribution from solute-solvent interactions to be separated from strictly intramolecular contributions to T 1 . The results in the polyatomic SCFs are compared to data in Ar. The density functional/thermodynamic theory 1 has been extended to include contributions at large wavevector (k). Very good, quantitative agreement between theory and data taken in ethane and fluoroform is achieved, but the agreement for data taken in carbon dioxide, while reasonable, is not as good. The theory uses a variety of input information on the SCF properties obtained from the fluids' equations of state and other tabulated thermodynamic data. The solute-solvent spatial distribution is described in terms of hard spheres. The theory is able to reproduce the data without solute-solvent attractive interactions or clustering in the calculation of the spatial distribution.
Picosecond infrared vibrational echo measurements from 60 to 300 K
on CO bound to the active site of a
mutant myoglobin, H93G(N-MeIm), are presented and
compared to measurements on native myoglobin and
on the mutant H64V. Although in H93G(N-MeIm) (the
proximal histidine replaced by glycine, with exogenous
N-methylimidazole in the proximal histidine pocket,
covalently bound to Fe), the only covalent linkage between
heme−CO and the protein is broken, there is no change in the
temperature-dependent vibrational pure dephasing
time, T
2*. The results demonstrate that
severing the only covalent bond between the heme and the
globin
has little or no effect on the protein dynamics detected by vibration
of the CO at the active site of myoglobin.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.