High-resolution optical spectroscopy of benzophenone under high pressure

Phosphorescence spectra of benzophenone have been investigated with a diamond anvil cell. At 2 K the spectra remain sharp under high pressure. The pressure shift of the origin exhibits a plateau around 25 kbar. This and other spectral observations are interpreted.     

Raman spectroscopy of vapors at elevated temperatures

The most effective way to obtain high quality vapor-phase Raman spectra is to heat the samples to increase their vapor pressure. Many samples can be heated to 350 °C and higher without decomposition. We have designed a simple Raman cell to allow these high temperature studies to be carried out. The high-temperature Raman spectra of nine molecules will be presented and discussed. Most of these are non-rigid molecules containing aromatic rings for which vibrational potential energy surfaces have been determined from their spectra. Two molecules (p-cresol and 3-methylindole) are model compounds for amino acids and their vapor-phase spectra are characteristic of environments with no hydrogen bonding.     

Development of a stabilized low temperature infrared absorption cell for use in low temperature and collisional cooling experiments

We have constructed a stabilized low temperature infrared absorption cell cooled by an open cycle refrigerator, which can run with liquid nitrogen from 250 to 80K or with liquid helium from 80K to a few kelvin. Several CO infrared spectra were recorded at low temperature using a tunable diode laser spectrometer. These spectra were analyzed taking into account the detailed effects of collisions on the line profile when the pressure increases. We also recorded spectra at very low pressure to accurately model the diode laser emission. Spectra of the R(2) line in the fundamental band of 13CO cooled by collisions with helium buffer gas at 10.5K and at pressures near 1 Torr have been recorded. The He-pressure broadening parameter (gamma(0) = 0.3 cm(-1) atm(-1)) has been derived from the simultaneous analysis of four spectra at different pressures.     

“原位”红外光谱追踪反应条件下催化体系的变化

为了观察和监测反应条件下中间产物和催化剂的变化,自行设计并安装了高温高压红外流动池。池体用不锈钢制成,窗口材料为NaCl或CaF₂。它可承受100atm和200℃。整个测量系统包括高压釜、循环泵、红外池等。用Microlab-600型红外分光光度计记录图谱。池内温度和压力与反应釜桐同,可对反应液体、气体或气液混合物进行"原位"追踪。当用铑膦络合物催化剂进行丙烯氢甲酰化反应时,在近于工业反应条件下(t=10O℃,P=17atm,正丁醛溶剂),检测到催化剂母体Rh(acac)(CO)(PPh₃)转化为活性物种RhH(CO)₂(PPh₃)₂;在合成气压力较低时,只转化为RhH(CO)(PPh₃)₃;此活性物种随催化剂失活而消失。催化剂加氧失活后,检测到配位体三苯基膦氧化为氧化三苯基膦,催化剂生成二聚物,丙烯氧化成丙酮,追踪到原料气CO氧化为CO₃的动态过程。本文对"原位"红外光谱实验方法、高温高压红外池作了介绍,并给出有关实验数据和结果。     

New experimental set-ups for studying nanoconfined water on the AILES beamline at SOLEIL

Three ensembles designed to investigate condensed matter in complex environments have been developed recently on the AILES beamline at SOLEIL. They have been exploited for studies aiming at understanding the properties of water molecules and their network in various confining systems, namely:

• -a hydration and temperature-controlled cell for the study of water confined in nanoporous Vycor,
• -a high pressure set-up allowing the study of the evolution of water molecules network trapped in Faujasite through the pressure-induced amorphisation of the matrix material,
• -a temperature resolved electrochemical cell used to record FIR difference spectra of metalloproteins interacting with water molecules.

By combining the high infrared flux and collimation of the AILES beamline with these optimized sample environments, it is possible to measure the infrared and THz spectra for minute quantities of samples in precise physical conditions.     

Identification of the diamond-like B-C phase by confocal Raman spectroscopy

The new diamond-like B-C phase was obtained from the graphite-like BC phase in a laser-heated diamond anvil cell at high temperature 2230+/-140 K and high pressure 45 GPa. Raman spectra of the new phase measured at ambient conditions revealed a peak at 1315 cm(-1), which was attributed to longitudinal-optical (LO) mode. The X-Y Raman mapping was used to investigate spatial distribution of the diamond-like phases and was shown to be a powerful tool in studying the sp(2)-to-sp(3) phase transformations occurring in the diamond cell under high temperature and high pressure.     

Pressure-tuning infrared and Raman spectroscopy of group 14 tetraphenyl compounds

The effect of high external pressures on the vibrational spectra of the tetraphenyl Group 14 compounds, Ph4M (M = Si, Ge, Sn, Pb), were examined between ambient pressure and 40 kbar with the aid of a diamond-anvil cell. The four compounds displayed similar behaviour as the pressure was increased and a structural transition at approximately 15 kbar, most probably associated with a phenyl ring rotation, was identified in each case. The pressure dependencies of selected vibrational modes were obtained.     

Determination of α and f for k0-NAA in irradiation sites with high thermalized neutrons

We have measured the ⁵⁷Fe Mössbauer spectra of the Hofmann pyridine complex Fe(pyridine)₂Ni(CN)₄ sample before and after exposure to high pressure of gaseous xenon. The temperature dependence of the high spin molar fraction has been determined from the ⁵⁷Fe Mössbauer spectra. The spin transition of the sample without the high pressure treatment occurs between 175 and 220 K with a hysteresis width of 15 K. Although the ⁵⁷Fe Mössbauer spectra suggest that the spin crossover behavior of the sample before and after the high pressure treatment are almost the same, the hysteresis of the latter sample is somewhat larger.     

High-pressure vibrational study of the catalyst candidate cis-dimercaptobis(triphenylphosphine)platinum(II), cis-[(Ph3P)2Pt(SH)2

Infrared and FT-Raman spectra of cis-dimercaptobis(triphenylphosphine)platinum(II), cis-[(PPh3)2Pt(SH)2], have been measured at high external pressures up to 55 kbar with the aid of a diamond-anvil cell (DAC). The wavenumber (v) versus pressure (P) plots from the Raman data indicate the occurrence of a pressure-induced phase transition at around 15 kbar. The metal-ligand stretching mode, v(Pt-S), and the C-H stretching mode of the phenyl rings, v(C-H), are highly sensitive to the application of pressure (dv/dP approximately 1.0 cm(-1) kbar(-1)). The IR results are generally consistent with the Raman data. The pressure-induced phase transition is most probably attributable to the reorientation of the phenyl rings in the complex; similar results have been obtained for other phenyl derivatives.     

A low voltage ion transport system for external ionization fourier transform mass spectrometry

An efficient ion transport system that interfaces external ion sources with a commercial dual-cell Fourier transform mass spectrometry (FTMS) system so as to retain maximum experimental flexibility has been constructed. Electrostatic lenses were used for ion transfer with potentials less than 200 V to preclude discharges. Spectra were recorded by thermal ionization and by electrospray ionization. Other high pressure ionization methods can be easily added to the external ion source chamber, making this a general solution for ion transport into an FTMS system. The efficiency of ion transfer was measured to be approximately 30%. A pressure ratio of 10⁵ between the external ion source chamber and the second cell has been demonstrated. The system incorporates a computer-controlled gate valve to isolate the cell regions from the external ion source chamber, permitting optimal conditions for ion injection and accumulation, and then after closing the valve, recording spectra at low pressure with high resolution. Spectra of Gramicidin S (resolution 90,000 at m/z 1164), aprotinin (resolution 410,000 at m/z 1304), and horse heart cytochrome c (resolution 50,000 at m/z 1546) are shown.     

Structural and vibrational characterization of tetracyanoethylene-hexamethylbenzene as a function of pressure

The neutron powder diffraction and inelastic neutron scattering (INS) spectra of the electron donor-acceptor complex, tetracyanoethylene-hexamethylbenzene have been studied as a function of pressure to 0.414 GPa. Using the PW91 and PBE density functional theories, the unit cell vectors were calculated as a function of pressure and are compared to those experimentally obtained from the diffraction data. The calculated lattice vectors display large errors at low pressures but were found to be in close agreement with the experimental vectors at 0.414 GPa. Comparison of the experimental INS spectra of the TCNE-HMB enabled assignment of specific vibrational modes while providing a direct measurement of the effect of pressure on the complex. The PW91 vibrational frequency calculations reproduced both the vibrational intensities and frequencies with relative accuracy.     

A high pressure FT-IR spectroscopic study of phase transitions in 1-chloro- and 1-bromoadamantane

The infrared spectra of two orientationally disordered adamantane derivatives, 1-chloro- and 1-bromoadamantane, have been obtained as a function of pressure by use of a diamond anvil cell. Phase transitions were detected from the splittings of vibrational bands and from changes in the slopes on plots of frequency versus pressure. In 1-chloroadamantane, a disorder-order phase transition was detected at approximately 5 kbar. This high-pressure phase is identical to the ordered phase obtained at low temperature. A second phase transition at high pressure was identified, for the first time, at approximately 17 kbar. The new high-pressure phase is an ordered phase. For 1-bromoadamantane, a semi-ordered to ordered phase transition was detected at about 5 kbar, and no other transitions were observed up to a pressure of 35 kbar. For both derivatives, the phase changes were reversible.     

Raman study of a new high pressure phase of hydrogen sulfide

Raman spectra of a new solid phase of H₂S, stable at high pressures and low temperatures, are reported. The number of observed peaks is indicative of a smaller unit cell than phase III that exists at zero pressure and low temperature. The dependence of both molecular and lattice mode frequencies on pressure is also investigated.     

High-resolution infrared spectroscopy of HCN-Znn (n = 1-4) clusters: structure determination and comparisons with theory

High-resolution infrared laser spectroscopy has been used to obtain rotationally resolved spectra of HCN-Zn(n) (n = 1-4) complexes formed in helium nanodroplets. In the present study the droplets passed through a metal oven, where the zinc vapor pressure was adjusted until one or more atoms were captured by the droplets. A second pickup cell was then used to dope the droplets with a single HCN molecule. Rotationally resolved infrared spectra are obtained for all of these complexes, providing valuable information concerning their structures. Stark spectra are reported and used to determine the corresponding permanent electric dipole moments. Ab initio calculations are also reported for these complexes for comparison with the experimental results.     

Structural, electronic, and optical properties of crystalline iodoform under high pressure: a first-principles study

The high pressure phases, electronic structure, and optical properties of iodoform at zero temperature have been investigated by first-principles pseudopotential plane-wave calculations based on the density-functional theory. A new high pressure polar monoclinic structure with space group Cc, denoted as β phase, has been observed after a series of simulated annealing and geometry optimizations. Our calculated enthalpies showed that the transition from α to β phase occurs at 40.1 GPa. Electronic structure calculated results showed that the insulator-metal transition in α phase due to band overlap is found at about 32 GPa. In addition, the calculated absorption spectra of iodoform are consistent with the experimental results.     

Vibrational spectroscopy at high pressures—LVI. A Raman study of some alkali metal halates,and the X-ray compressibility of KClO3

Raman spectra at high pressure have been obtained for KBrO₃, NaClO₃ and NaBrO₃ in a diamond anvil cell. A phase change has been found for KBrO₃ at 19 kbar; at 24 kbar for NaBrO₃; and at 36 kbar for NaClO₃. The bulk compressibility of KClO₃ has been determined by X-ray diffraction using synchrotron radiation and found to be 2.36 × 10⁻² GPa⁻¹, in good agreement with Bridgman's value.     

Characterization of a high-pressure quadrupole collision cell for low-energy collision-indneed dissociation

A RF-only quadrupole collision cell of new design has been evaluated for use in tandem mass spectrometry experiments as a component of a triple quadrupole mass spectrometer. The new design permits operation at values of collision gas thickness higher by 1 order of magnitude than those used in most cells of this type. When operated at sufficiently high collision gas pressures, the transmission efficiency for precursor ions increases with increasing pressure, often to values greater than those observed in the absence of collision gas. Simultaneously, the attainable resolving power for fragment ions across the entire mass-to-charge ratio range, even for multiply charged precursors, also increases to the point where isomers of a quadruply charged fragment are resolved. The performance of the cell, judged in terms of yields and resolution of fragment ions, has been investigated as a function of the nature and pressure of collision gas, the kinetic energy of the precursor ions that enter the cell, and of the size and charge state of the precursors. The enhanced performance is explicable in terms of a marked deceleration of all ions that emerge from the cell to very low energies, probably a few tens of millielectronvolts, so that the cell effectively acts as an ion source for the second mass filter (fragment ion analyzer) to provide a spectrum of ions of fixed axial energy. The high transmission efficiency appears to arise from a collisional focusing effect analogous to that exploited in three-dimensional RF ion traps. The low axial energies imply that ion transit times through the cell are sufficiently long (several milliseconds) that, in precursor ion experiments where the first mass filter is scanned, a hysteresis effect is observed. This implies that in this operating mode compromises must be sought between scan speed and quality of peak shape. Examples are given of spectra obtained under realistic operating conditions that employ flow injection of samples.     

Measurement of circular dichroism spectra of liquid/liquid interface by centrifugal liquid membrane method.

The direct measurement of the circular dichroism (CD) spectra of liquid/liquid interface has been achieved for the first time by the centrifugal liquid membrane (CLM) method combined with a conventional CD spectropolarimetry. In the sample chamber of the CD spectropolarimeter, a cylindrical glass cell containing small amounts of organic and aqueous phases was rotated at ca. 7000 rpm to generate a two-phase liquid membrane with a high specific interfacial area. The CD spectra of the J-aggregate of protonated 5,10,15,20-tetraphenylporphyrin formed at the toluene/sulfuric acid interface in the rotating cell have been measured. The results demonstrated the novelty and advantages of this method.     

Size dependence of the solid-solid phase transition in CdSe nanocrystals

High pressure optical absorption spectra are presented for CdSe nanocrystals as a function of size. The spectra show a transition to a high pressure Rock Salt type phase at pressure greatly elevated from the bulk. The size dependence of the transition pressure can be explained in part by an increased surface tension in the Rock Salt phase relative to the low pressure tetrahedral phase.     

Optical transient absorption spectroscopy of LaO produced by pulsed laser ablation of La2O3

Temporally and spatially resolved absorption spectrometry has been used to study molecular LaO absorption in laser ablated plume from an La2O3 target The absorption time-of-flight (TOF) spectra of ground-state LaO molecules were measured The TOF spectra indicate that only one component is observed in vacuum and in an Ar ambient, while there are two component, a fast and a broad slow component, observed at higher O2 pressure. The absorbance of LaO molecules decreases gradually with increasing ambient gas pressure. The dependence of the absorbance of LaO on the detection distance can be fitted by an exponential decay equation. The shock wave model is used to describe the behavior of ground state LaO molecules in high O2 pressure region.