Raman diamond anvil cell

New metliods appear regularly. The principal challenges to the ingenuity of the spectroscopist are availability of appropriate radiation sources, absorption or distortion of the radiation by the windows and other components of the high-pressure cells, and small samples. Lasers and synchrotron radiation sources are especially valuable, and use of beryllium gaskets for diamond-anvil cells will open new applications. Impulse-stimulated Brillouin [75], coherent anti-Stokes Raman [76, 77], picosecond kinetics of shocked materials [78], visible circular and x-ray magnetic circular dicliroism [79, 80] and x-ray emission [72] are but a few recent spectroscopic developments in static and dynamic high-pressure research. 

Chronister E L and Crowell R A 1991 Time-resolved coherent Raman spectroscopy of low-temperature molecular solids in a high-pressure diamond anvil cell Chem. Phys. Lett. 182 27... 

Raman spectroscopy with high pressure windowed cell (Sum et al., 1997 Thieu et al., 2000) P, T and hydrate phase Yes P, P, hydrate phase vs. time (mins) Typically for sapphire window < 10,000 psi (for capillary tubes <60,000 psi diamond anvil cell GPa s) Guest occupancy ratios, structure, structural transitions... 

Figure 3-5 Raman spectra of Mn2(CO)10 at (A) ambient pressure and (B) 16kbar, and of Re2(CO)10 at (C) ambient pressure and (D) 16kbar in diamond anvil cell. (Reproduced with permission from Ref. 13.)...

Infrared and Raman studies at very high pressure (up to several hundred kbar) are carried out fairly routinely with diamond anvil cells (DAC). The DAC, which was first developed for high-pressure infrared absorption measurements by Weir et al. (1959) and for X-ray studies by Jamieson et al. (1959), has become a very powerful tool for a wide variety of ultra-high pressure investigations, with particularly important applications in solid state physics. The potential of the method has increased enormously with the introduction of gaskets into the DAC by Van Valkenburg (see Jayaraman, 1983) and with the possibility of pressure calibration by the ruby fluore.scence method (Forman et al, 1972). 

Technology exists to measure spectra at pressures higher than 10 bar using diamond anvil cells. Raman and IR techniques see Vibrational Spectroscopy) are most often brought into play in pressure-dependent spectroscopies. Temperature-dependent spectroscopy at high pressures is also possible. ... 

Ammonium dinitramide and dinitro azetidinium dinitramide For both of these materials the pressure/temperature and reaction phase diagram have been determined using a high-temperature-high-pressure diamond anvil cell with FTIR spectroscopy, Raman spectroscopy and optical microscopy. For ammoninm dinitramide energy dispersive X-ray diffraction was also employed (Russell et al. 1996, 1997). 

We have made direct optical observations and measmements of microbial activity at various pressures. As in the above experiments, we have used diamond anvil cells in combination with micro-Raman spectroscopy and optical microscopy to directly monitor their viability and metabolic activity at extreme conditions [58]. The following is an overview of these direct observations of microbial activity under extreme pressures and their implications for adaptive mechanisms of life (as we know it) on this planet. 

Figure 11. Raman spectra of the formic-biological system (A) shown with the vibration peaks of formic and diamond anvils used in this study. The outlined boxed region is shown at higher resolution (B) to quantify the successive decrease in the peak intensity of the C-H stretch of formic acid at pressures of 68,142, and 324 MPa. The equivalent formate concentrations (C), corresponding to each peak height change, are based on comparisons with a known calibration curve. All experiments were performed at 25°C, with diamond anvil cells with gold-lined sample chambers. Pressures were estimated using Raman shifts in quartz used as an internal calibrant.

Pressure was generated with a diamond anvil cell (DAC) employing beveled anvils with central flats ranging from 20 to 100 jim and flat diamonds with 200-500 pm culets. Two types of DAC were used modified (to match a continuous flow He cryostat) Mao-Bell cell for operations at room and low temperatures [41] and a Mao-Bell high-T external heating cell [42]. The latter one is equipped with two heaters and thermocouples. Four experiments were performed at RT aiming to highest pressure and the final pressures varied from 180 to 268 GPa. For low-temperature measurements we used a continuous-flow He cryostat, which allowed infrared and in situ Raman/ fluorescence measurements. More details about our IR/Raman/fluorescence setup at the NSLS are published elsewhere [41]. 

Raman and Fluorescence Spectroscopic Analysis of Samples in a Diamond Anvil Cell... 

Fig. 4.19 Raman spectra of Sii36 collected during compression up to 8 GPa. Asterisks mark peaks that are not identified as part of the Sii36 Raman spectrum and may be due to impurities within the sample compressed within the diamond anvil cell (from [66])...

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