Raman Spectra from Partially Deuterated Water and Ice VI to 10.1 kbar at 28 degrees C

High-pressure argon-ion laser-Raman spectra (4880 angstrom excitation) have been obtained from partially deuterated water and ice VI ( 20 volume % D(2)O) in the OD and OH stretching regions to pressures of 10.1 kbar at 28 degrees C The Raman spectra from ice VI are the first to be reported at room temperature, and they are similar to the liquid spectra obtained at 9.7 kbar. Raman shifts corresponding to contour intensity maxima were observed to change with pressure rise in the O D and OH stretching regions from Delta(nu) over bar 2513-2490 cm(-1) and Delta(nu) over bar = 3402-3380 cm(-1), respectively, for pressures from 1 bar to 10.1 kbar ( ice VI). In addition, a shoulder observed at 1 bar on the OD contour near Delta(nu) over bar = 2650 cm(-1) became less distinct and was visually absent for pressures from 6.4 to 10.1 kbar, although a shoulder on the OH contour at about Delta(nu) over bar = 3250 cm(-1) intensified gradually for pressures to 9.7 kbar, and abruptly upon freezing at 10.1 kbar. The small effects of pressure on the O D component percentages obtained from computer analysis indicate that hydrogen-bond breakage is not a significant effect of pressure rise, and a downward change in the position of the OD stretching component having the largest Raman shift indicates that the nonhydrogen-bonded O D units or broken O-D center dot center dot center dot O bonds that exist at 1 bar are probably transformed by close packing due to compression into weak O-D center dot center dot center dot O bonds that are angularly deformed. In addition, intensification of the OH component at Delta(nu) over bar = 3220 cm(-1) upon freezing or upon pressurizing the liquid to 9.7 kbar is indicated by the computer analyses, and an increase in intermoleeular coupling is thus favored, as opposed to enhancement of Fermi resonance, because the positions of components at Delta(nu) over bar = 3220 cm(-1) and Delta(nu) over bar = 3405 cm(-1) are nearly independent of pressure. The computer results also strengthen previous evidence indicating that the OD component which occurs at about, Delta(nu) over bar = 2654 cm(-1) at 1 bar arises from broken O-D center dot center dot center dot O bonds, when it is understood that the severely deformed O-D center dot center dot center dot O bonds. of ice VI give rise to intensity at a Raman shift of Delta(nu) over bar = 2617 cm(-1), a difference of 37 cm(-1) in the direction of stronger hydrogen-bonding.