Abstract
Pressure-induced structural change in molecular systems has demonstrated strong promises to access previously unexplored, novel structures and new properties in molecular materials with practical applications. The in situ structural characterization is of fundamental importance to understand the exotic structures and the possible transformation mechanisms. Among all the spectroscopic probes, vibrational spectroscopy that include Raman and Fourier-transform infrared (FTIR) spectroscopy and microscopy allow for highly efficient, sensitive and qualitative characterization of pressure-induced new structures and transformation processes in situ. Supported by state-of-the-art, highly customized spectroscopic systems in-house and at synchrotron facilities, molecular structures and materials properties can be probed in a broad pressure-temperature range with very high spectral and spatial resolutions. Complementary to each other, Raman and IR spectroscopy provide valuable information in molecular structures, nature of bonding, lattice dynamics as well as intermolecular interactions. In this chapter, a comprehensive and critical review of examples of pressure-induced molecular transformations in a wide variety of molecules and materials probed by vibrational spectroscopy is provided. The purpose of this chapter is to give readers the most recent advances in high-pressure chemistry and materials research by demonstrating the power of vibrational spectroscopy as a highly effective in situ structural characterization tool.
Keywords
- high pressure
- diamond anvil cells
- Raman spectroscopy
- FTIR spectroscopy
- conformation
- hydrogen bonding
- phase transitions
- guest-host interactions
1. Introduction
As one of three principal thermodynamic variables, pressure (P) plays an important role to alter the interatomic distances and thus the nature of intermolecular interactions, chemical bonding, molecular configurations, crystal structures and stability of materials. Extreme pressure can even induce transformations involving the strongest chemical interactions that exceed 10 eV (965 kJ mol−1) such that chemical bonds and even the well-known properties of atoms and molecules can be completely changed. As a result, investigation of pressure-induced structural transformations and formation of novel functional materials has become a vibrant frontier in chemistry and materials science [1]. On one hand, major advances in high-pressure techniques such as diamond anvil cell have allowed the study of molecules and materials in an unprecedented pressure-temperature (P-T) range. On the other hand, the compatible micro-spectroscopic probes have made possible the characterization of structures and transformational processes
Among all the available
2. Experimental methods
2.1. The diamond anvil cell
The recent advances in high-pressure technology have enabled the generation of extreme conditions in a broad P-T range with great controllability and accuracy. In particular, diamond anvil cell (DAC) is a fundamental apparatus to achieve static high pressures. Diamonds are known as the hardest material in nature and thus suitable as anvils to generate very high pressure. Moreover, diamonds are transparent to a wide spectral range of electromagnetic radiation from far-IR to hard X-ray. As a result, various analytical probes, including optical spectroscopy, synchrotron and neutron sources, have enabled structural characterization of material under extreme P-T conditions with unprecedented spatial, temporal and spectral resolutions.
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig1.png)
Figure 1.
Schematic diagram of a diamond anvil cell.
Figure 1 shows a typical DAC apparatus where two brilliant cut diamonds are used as anvils to exert static pressure up to several million atmospheres (or several hundred GPa) with only moderate force. A metal gasket with a hole drilled at the center serves as the sample chamber. Most of the time the sample to be studied is loaded together with pressure-transmitting medium (PTM) to enhance the hydrostaticity, and a ruby chip which is used for pressure calibration. The extreme pressures can be accurately determined by monitoring ruby fluorescence lines using the following relationship [9]:
where
To conduct vibrational spectroscopy on materials loaded in DAC effectively, optical transparency is a prime factor in selecting diamond anvils. Two types of diamonds (i.e., type I and type II) are typically used for different spectroscopic probes. Both types have the intense first-order Raman line at 1332 cm−1 (
2.2. Raman spectroscopy
Raman spectroscopy is a vibrational spectroscopy based on the inelastic scattering of visible photons (typically from a laser source) by materials, a process with a much smaller cross-section than other spectroscopic processes (e.g., absorption, fluorescence, etc.). Although many commercial Raman microscopy systems are available, they generally have a rigid design that does not allow
2.3. FTIR spectroscopy
Complementary to Raman spectroscopy, IR absorption spectroscopy provides sensitive and fingerprints information on materials loaded in DAC, especially those with high fluorescence that prohibits effective Raman measurements. The IR measurements for the examples demonstrated in this chapter were mostly carried out using a customized IR micro-spectroscopy system constructed in-house [11]. Specifically, a commercial FTIR spectrometer (model Vertex 80v from Bruker Optics Inc.) containing a Globar IR source constitutes the major component of the micro-IR system. The spectrometer is operated under a vacuum of <5 mbar to efficiently remove the absorption by H2O and CO2. The IR beam is collimated with varying diameters achieved by using apertures from 0.25 to 8 mm, and then is directed into a relay box through a KBr window. Using the combination of iris optics and 15× reflective objective lens (numerical aperture of 0.4), the IR beam is then focused onto the sample in the DAC. Using an XYZ precision stage with the aid of an optical microscope equipped with a 20× eyepiece from Edmond Optics and an objective lens of variable magnifications, the sample loaded in DAC can be easily aligned to allow the maximum transmission of the IR beam. Using a series of iris apertures, the size of the IR beam was set to be identical to the entire sample size (e.g., ~200 μm). Another identical reflective objective as the condenser is used to collect the transmitted IR beam, which is subsequently directed to a midband mercury cadmium telluride (MCT) detector. A ZnSe window equipped on the midband MCT detector allows efficient measurements in the spectral range of 600–12,000 cm−1. The combination of 512 scans and a resolution setting of 4 cm−1 is typically used for each spectrum measurement that gives an excellent signal-to-noise ratio. The absorption of diamond anvils loaded with KBr but without any sample is used as the reference spectrum, which is divided as background from each sample spectrum to obtain the absorbance.
2.4. Synchrotron-based FTIR spectroscopy
Synchrotron light is a source of electromagnetic radiation produced by a storage ring housing traveling electrons with a near speed of light. Although synchrotron source provides enormous advantages typically in the X-ray region, the infrared synchrotron light has unique applications for DAC-based measurements due to the very intense, very broad and highly focused IR source that allows very high spatial resolution and far-IR measurements. Some examples in this chapter are based on the experiments performed at the U2A beamline at the National Synchrotron Light Source (NSLS) of Brookhaven National Laboratory (BNL). Briefly, the IR beam from the synchrotron storage ring is first extracted through a wedged diamond window from a source with a 40 × 40 mrad solid angle. Then it is collimated to a 1.5″ diameter beam and directed into a vacuum FTIR spectrometer (Bruker IFS 66V) equipped with three independent microscope systems. The spectrometer is equipped with a number of combinations of IR beam splitters and detectors (e.g., silicon bolometer and MCT). For mid-IR measurements, a Bruker IR microscope is used to focus the IR beam onto the sample. The absorption spectrum is collected in transmission mode by the MCT detector in the spectral range of 600–4000 cm−1. The far-IR spectra are collected using a customized IR microscope allowing very high collection efficiency and recorded by the bolometer in the spectral region of 100 to 600 cm−1. A resolution of 4 cm−1 was used in all IR measurements. For all measurements, mid-IR spectra were collected through a 30 × 30 μm2 aperture, whereas the effective IR transmission area covered the entire sample (i.e., a circle of about 90 μm in diameter) for the far-IR measurements. The data acquisition, processing and analysis are similar to those obtained using the in-house mid-IR spectroscopy system.
3. Pressure-induced conformational change
Pressure-mediated conformational equilibrium is of particular interests because the reactivity of many organic reagents, product yields, and even reaction pathways are strongly correlated with molecular conformations. Here, two simple halogen substituted alkane molecules, that is, 1,2-dichloroethane (DCE) [12] and chlorocyclohexane (CCH) [13], were investigated under high pressures for conformational and structural changes using
3.1. 1,2-Dichloroethane
As a model molecule, DCE has two representative conformations, that is,
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig2.png)
Figure 2.
Representative Raman spectra of DCE on compression in the pressure region of (a) 0–5.0 GPa and (b) 5.7–29.2 GPa and the spectral region of 120–1300 cm−1 and 2900–3100 cm−1. The assignments of Raman active mode are labeled below for
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig3.png)
Figure 3.
Representative Raman spectra of DCE in the magnified spectral region of 600–800 cm−1 for fluid phase. The inset is the plot of logarithm of relative intensities of the first two peaks over the third peak as a function of pressure. Reproduced with permission from reference [
3.2. Chlorocyclohexane
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig4.png)
Figure 4.
(a) Raman spectra of CCH collected at ambient pressure (top) in comparison with that collected upon slight compression (i.e., at 0.03 GPa, bottom). CCH exists as a mixture of axial and equatorial conformer with the latter dominant at condition and thus the assignment labeled above each Raman modes refers to equatorial conformation for the top spectrum. Axial and equatorial conformers share majority of common Raman modes and thus only those exclusively associated with axial conformer are labeled in the bottom spectrum. (b) Selective Raman spectra of CCH on compression in the pressure region 0–14 GPa in the spectral range of 120–1300 cm−1 and 2800–3200 cm−1. Reproduced with permission from reference [
4. Pressure-mediated hydrogen bonding
Hydrogen bonding plays an important role in stabilizing a wide range of molecular structures and influences the chemical and physical properties of molecular systems. Typically, the characterizations of hydrogen bonding are inferred from crystal structures or by theoretical modeling. Here two examples are shown to demonstrate that vibrational spectroscopy on materials loaded in DAC can reveal interesting pressure-mediated hydrogen bonding interactions.
4.1. Ethylene glycol
Ethylene glycol (EG) serves as a prototype for understanding hydroxyl group interactions in biological compounds such as sugars and polysaccharides. Using
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig5.png)
Figure 5.
Infrared absorption spectra of ethylene glycol at different pressures under compression in the spectral region of 2500–4000 cm−1 (a) and variation of OH stretching infrared active modes of ethylene glycol with pressure (b). Reproduced with permission from reference [
4.2. Bis(1H-tetrazol-5-yl)amine monohydrate
Bis(1H-tetrazol-5-yl)amine (BTA) with two tetrazole rings linked by one nitrogen atom that contains 82.5 wt% nitrogen has been considered a promising high energy density material. Moreover, examining the possibility of converting this high nitrogen content precursor to other polymorphs with higher energy density using high pressure is of great interest.
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig6.png)
Figure 6.
Pressure dependence of IR modes of BTA⋅H2O on compression. Reproduced with permission from reference [
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig7.png)
Figure 7.
Normalized unit cell volume versus pressure (black squares) for BTA⋅H2O on compression and fitted equation of state (red curve) using second-order Birch-Murnaghan equation. The inset shows normalized monoclinic unit cell parameters for
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig8.png)
Figure 8.
Proton hopping and molecular interactions of BTA⋅H2O system based on first-principles simulations.
5. Structural and phase transitions
5.1. Boron nitride nanotubes
Compared to carbon nanotube, boron nitride nanotube (BNNT) has structure-independent wide band gap, enhanced thermal stability, high resistance to oxidation at high temperatures, high thermal conductivity and remarkable yield strength, making it a promising advanced material for a wide range of applications. Multiwalled boron nitride nanotubes (BNNTs) were compressed at room temperature in diamond anvil cells up to 35 GPa followed by decompression and characterized by
![](http://cdnintech.com/media/chapter/52018/1512345123/media/Fig9.png)
Figure 9.
Infrared spectra of BNNTs at selected pressures upon compression (red lines) and decompression (blue lines) in the spectra region of 600–1900 cm−1. The solid and dashed arrows indicate the compression and decompression sequence. The inset shows spectra from another run at a highest pressure of 34.6 GPa on compression (red line) and complete pressure release (blue line). Reproduced with permission from reference [
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig10.png)
Figure 10.
Pressure dependence of representative IR modes of BNNTs (open symbols) and in comparison with those for bulk h-BN (solid symbols) on compression. The squares and circles are the respective A2u and E1u modes of h-BN structure, while other symbols represent IR modes for w-BN structure. The dashed line at around 11 GPa denotes the transition onset for both BNNTs and bulk h-BN. The vertical bars for A2u mode represent the full width at half maximum for BNNTs. The inset shows the ratio of the IR band intensity of the mode at 1125 cm−1 for w-BN over the E1u mode for h-BN observed in BNNTs labeled as Iw/Ih. The solid lines are for eye guidance showing three distinctive conversion regions. Reproduced with permission from reference [
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig11.png)
Figure 11.
Crystal structures and bonding patterns of (a) h-BN and (b) w-BN with the transformation conditions for BNNTs and bulk h-BN denoted. The red and blue balls represent boron and nitrogen, respectively. The dashed arrow for BNNT indicates incomplete irreversible transformation, while the solid arrows with different length for bulk h-BN indicate partial reversibility. Reproduced with permission from reference [
5.2. Aromatic compounds
Aromatic compounds have been investigated under non-ambient conditions over the past few decades due to their great importance in both fundamental and applied science. In particular, they have been widely studied in chemical synthesis under elevated temperatures and pressures as the precursors of technological materials, such as amorphous solids and conjugated polymers [16]. For instance, using
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig12.png)
Figure 12.
Selected Raman spectra of pyridine on compression in the spectral region of 60–500 cm−1 (a), 400–1160 cm−1 (b) and 1100–3300 cm−1 (c). Reproduced with permission from reference [
5.3. Metal and chemical hydrides
High-pressure investigations of potential hydrogen storage materials, especially hydrogen-rich metal and chemical hydrides have received increasing attentions [8]. Not only has pressure demonstrated great promises for producing new structures and materials but also many known hydrogen-rich materials have exhibited new transformations as well as totally different thermodynamic and kinetic behaviors under higher pressures than under ambient conditions. Hydrides in a wide range of different categories, such as calcium borohydride, sodium amide and ammonia borane, have been extensively investigated under high pressures by vibrational spectroscopy, X-ray diffraction and theoretical calculations [18–21]. Here ammonia borane (NH3BH3) is chosen as an example to demonstrate that vibrational spectroscopy can be an effective tool to elucidate novel high-pressure structures [18, 21].
Using
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig13.png)
Figure 13.
Pressure dependences of Raman shift of NH3BH3 on compression for (a) the lattice modes; (b) the 11B-N/10B-N stretch (ν5/ν5′) modes; and (c) the NBH rock (ν12a, ν12b, ν11a, ν11b and ν11c) modes. The solid lines crossing the solid symbols are based on linear fit. The vertical dashed lines indicate the proposed phase boundaries. Reproduced with permission from reference [
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig14.png)
Figure 14.
Selected Raman spectra of NH3BH3 collected on compression up to 15.92 GPa at 180 K in the region of 50–300 cm−1 (a), 1000–1300 cm−1 (b), and 3100–3400 cm−1 (c). The assignments are labeled for selected Raman mode at selected pressures. Reproduced with permission from reference [
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig15.png)
Figure 15.
Schematic P-T phase diagram of NH3BH3 in the pressure region of 0–15 GPa (in log2 scale) and temperature region of 80–350 K. Solid symbols are experimental data from this study, with squares for
Subsequently, ammonia borane was investigated at simultaneous high pressures (up to 15 GPa) and low temperatures (down to 80 K) by
6. Pressure-induced chemical reactions
6.1. Acrylic acid
Pressure-induced polymerization is a chemical process pertaining to green chemistry as the reactions can be carried out in the absence of any solvent or catalyst, which implies a lesser environmental impact. Poly(acrylic acid) is a well-known polymer with a wide variety of industrial applications such as being super absorbent materials, biocompatible polymers, poly-electrolytes and nanopolymers in molecular devices. Therefore, it is very significant in the polymer industry to explore pressure-induced polymerization from this monomer, as the polymer product with improved properties distinct from that obtained using conventional synthetic methods might be obtained. The first pressure-induced structural and polymeric transformations of acrylic acid were studied by
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig16.png)
Figure 16.
Raman spectra of acrylic acid at selected pressures upon compression in the pressure region of 0.3–4.5 GPa (a) and 3.3–10 GPa (b) in the spectral region of 100–1300 cm−1. Reproduced with permission from reference [
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig17.png)
Figure 17.
Raman spectrum of poly(acrylic acid) purchased from Aldrich with an average molecular weight of 1800 g/mol (a) and 450,000 g/mol (b) in comparison with that of recovered acrylic acid by decompression from 10 GPa (c) and that of acrylic acid at 10 GPa (d). Reproduced with permission from reference [
6.2. Ethylene glycol
Using combined high-pressure and photon excitations especially in the UV range has demonstrated strong potential to produce new molecular materials in a highly efficient way. Using multi-line UV radiation at ~350 nm, the photon-induced reactivity of liquid ethylene glycol (EG) at room temperature was investigated by FTIR spectroscopy [24]. Upon UV irradiation, IR spectra of EG show two sets of distinctive profiles after specific reaction time, indicating multiple photon-induced chemical reactions, which can be designated as primary and secondary processes (Figure 18). Careful spectral analysis allows the identification of primary reaction products that include glycolaldehyde, acetaldehyde and methanol. Further photoreactions of these primary products led to the formation of the secondary products, which were identified as methane, formaldehyde, methoxymethanol, methylformate and carbon dioxide. Based on these reaction products, possible reaction mechanisms and production pathways were proposed. We also found that the initial loading pressure of EG plays an important role in influencing the reaction kinetics as well as in controlling the accessibilities for some reaction channels such as for CH4 (Figure 19a). Quantitative analysis of the antisymmetric stretching mode of CO2 formed at different loading pressures suggests the formation of CO2 clathrate hydrates well as CO2 clusters. The stabilities as well as relative abundance of these CO2 species are found to be dependent on both pressure and radiation time (Figure 19b). These observations revealed interesting pressure-induced CO2 sequestration behaviors as a result of photochemical reactions of ethylene glycol.
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig18.png)
Figure 18.
Selected FTIR spectra of EG with an initial loading pressure of 0.1 GPa upon UV irradiation (with
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig19.png)
Figure 19.
Relative photochemical reaction yields of CH4 (a) and CO2 (b) derived by integrating the intensity of the respective characteristic IR modes (
7. Porous materials and guest-host interactions
7.1. ZIF-8
ZIF-8 is a representative member of the zeolitic imidazolate framework (ZIF) family, an emerging class of porous materials with promising applications in gas storage and catalysis, etc. As a result, substantial interest has been focused on the investigation of its structure and properties under different conditions. Pressure tuning has proven an important and effective means to modify the structures and thus the associated properties of porous materials. Therefore, ZIF-8 was investigated under high pressures up to ~39 GPa using
In a subsequent study, ZIF-8 framework was investigated when loaded with CO2 in a diamond anvil cell at high pressures of 0.8 GPa, far beyond the conventional gas adsorption pressure also using
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig20.png)
Figure 20.
Selected IR spectra of ZIF-8 on compression to a highest pressure of 1.60 GPa and as recovered (a), and to another highest pressure of 39.15 GPa and as recovered (b). Reproduced with permission from reference [
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig21.png)
Figure 21.
(a) The comparison of IR spectrum of pure CO2 (top), ZIF-8 loaded with CO2 (middle) and that of pure ZIF-8 (bottom) at similar pressures. The inset shows the spectral region for the combination modes of CO2 loaded with ZIF-8 loaded (top) and pure CO2 (bottom). (b) Photograph of ZIF-8 loaded with CO2 obtained under an optical microscope. The arrows denote the positions of the C═C stretching mode of the imidazole ring. Reproduced with permission from reference [
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig22.png)
Figure 22.
Far-IR spectra of empty ZIF-8 framework upon compression to 2.61 GPa and decompression to ambient pressure. These far-IR spectra suggest that pressure can significantly modify the crystal structures of empty ZIF-8 framework irreversibly. Reproduced with permission from reference [
7.2. MIL-68
As a promising candidate for the application of gas storage and separation, metal-organic framework (MOF) MIL-68 has unique structural topology that contains two types of channels with distinct pore sizes. Using
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig23.png)
Figure 23.
(a) IR spectra of activated MIL-68 (In) with PTM upon compression. (b) IR spectra of activated MIL-68 (In) and MIL-68 (In) loaded with CO2 at around 0.4 GPa in the frequency region of 600–3800 cm−1. (c) IR spectra of MIL-68 (In) loaded with CO2 upon compression. Reproduced with permission from reference [
![](http://cdnintech.com/media/chapter/52018/1512345123/media/fig24.png)
Figure 24.
Simulated contour plots of the CO2 probability density distributions along the hexagonal and triangular channels of MIL-68 (In) framework at (a) 1 bar, (b) 1000 bar or 0.1 GPa and (c) 105 bar (or 10 GPa). Reproduced with permission from reference [
8. Summary and future perspectives
In summary, this chapter demonstrated the application of
In addition to extreme pressure, extreme temperatures such as several Kelvin and several hundred degrees Celsius, and especially their combinations pose experimental challenges yet offer new and unexplored P-T domains for novel structures and properties of materials to be discovered.
Acknowledgments
This work was supported by a Discovery Grant, a Research Tools and Instruments Grant from the Natural Science and Engineering Research Council of Canada, a Leaders Opportunity Fund from the Canadian Foundation for Innovation, an Early Researcher Award from the Ontario Ministry of Research and Innovation, a Petro-Canada Young Innovator Award and by Defense Research and Development Canada under contract No. W7702-135601. The synchrotron IR measurements presented were performed at U2A beamline of National Synchrotron Light Source of US Brookhaven National Laboratory.
References
- 1.
Song Y, Manaa MR. New trends in chemistry and materials science in extremely tight space. J Phys Chem C. 2012; 116 :2059–60. - 2.
Hemley RJ, Ashcroft NW. The revealing role of pressure in the condensed matter sciences. Phys Today. 1998; 51 :26–32. - 3.
Hemley RJ. Effects of high pressure on molecules. Annu Rev Phys Chem. 2000; 51 :763–800. - 4.
Schettino V, Bini R. Molecules under extreme conditions: Chemical reactions at high pressure. Phys Chem Chem Phys. 2003; 5 :1951–65. - 5.
McMillan PF. Chemistry at high pressure. Chem Soc Rev. 2006; 35 :855–7. - 6.
Grochala W, Hoffmann R, Feng J, Ashcroft NW. The chemical imagination at work in very tight places. Angew Chem-Int Edit. 2007; 46 :3620–42. - 7.
Schettino V, Bini R. Constraining molecules at the closest approach: chemistry at high pressure. Chem Soc Rev. 2007; 36 :869–80. - 8.
Song Y. New perspectives on potential hydrogen storage materials using high pressure. Phys Chem Chem Phys. 2013; 15 :14524–47. - 9.
Mao HK, Bell PM, Shaner JW, Steinberg DJ. Specific volume measurements of copper, molybdenum, palladium, and silver and calibration of the ruby R1 fluorescence pressure gauge from 0.06 to 1 mbar. J Appl Phys. 1978; 49 :3276–83. - 10.
Dong Z. High-pressure study of molecular solids and 1D nanostructures by vibrational spectroscopy and synchrotron X-ray diffraction [Thesis]: University of Western Ontario; 2012. - 11.
Dong Z, Song Y. Transformations of cold-compressed multiwalled boron nitride nanotubes probed by infrared spectroscopy. J Phys Chem C. 2010; 114 :1782–8. - 12.
Sabharwal RJ, Huang Y, Song Y. High-pressure induced conformational and phase transformations of 1,2-dichloroethane probed by Raman spectroscopy. J Phys Chem B. 2007; 111 :7267–73. - 13.
Dong Z, Beilby NG, Huang Y, Song Y. Conformational and phase transformations of chlorocyclohexane at high pressures by Raman spectroscopy. J Chem Phys. 2008; 128 :074501. - 14.
Murli C, Lu N, Dong Z, Song Y. Hydrogen bonds and conformations in ethylene glycol under pressure. J Phys Chem B. 2012; 116 :12574–80. - 15.
Zhou L, Shinde N, Hu A, Cook C, Murugesu M, Song Y. Structural tuning of energetic material Bis(1H-tetrazol-5-yl)amine monohydrate under pressures probed by vibrational spectroscopy and X-ray diffraction. J Phys Chem C. 2014; 118 :26504–12. - 16.
Dong Z, Seemann NM, Lu N, Song Y. Effects of high pressure on azobenzene and hydrazobenzene probed by Raman spectroscopy. J Phys Chem B. 2011; 115 :14912–8. - 17.
Zhuravlev KK, Traikov K, Dong Z, Xie S, Song Y, Liu Z. Raman and infrared spectroscopy of pyridine under high pressure. Phys Rev B. 2010; 82 :064116. - 18.
Xie S, Song Y, Liu Z. In situ high-pressure study of ammonia borane by Raman and IR spectroscopy. Can J Chem. 2009; 87 :1235–47. - 19.
Liu A, Xie S, Dabiran-Zohoory S, Song Y. High-pressure structures and transformations of calcium borohydride probed by combined Raman and infrared spectroscopies. J Phys Chem C. 2010; 114 :11635–42. - 20.
Liu A, Song Y. In situ high-pressure study of sodium amide by Raman and infrared spectroscopies. J Phys Chem B. 2011; 115 :7–13. - 21.
Liu A, Song Y. In situ high-pressure and low-temperature study of ammonia borane by Raman spectroscopy. J Phys Chem C. 2012; 116 :2123–31. - 22.
Chen JH, Couvy H, Liu HZ, Drozd V, Daemen LL, Zhao YS, et al. In situ X-ray study of ammonia borane at high pressures. Int J Hydrogen Energy. 2010; 35 :11064–70. - 23.
Murli C, Song Y. Pressure-induced polymerization of acrylic acid: a Raman spectroscopic study. J Phys Chem B. 2010; 114 :9744–50. - 24.
Guan J, Song Y. Pressure selected reactivity and kinetics deduced from photoinduced dissociation of ethylene glycol. J Phys Chem B. 2015; 119 :3535–45. - 25.
Hu Y, Kazemian H, Rohani S, Huang Y, Song Y. In situ high pressure study of ZIF-8 by FTIR spectroscopy. Chem Commun. 2011; 47 :12694–6. - 26.
Hu Y, Liu Z, Xu J, Huang Y, Song Y. Evidence of pressure enhanced CO2 storage in ZIF-8 probed by FTIR Spectroscopy. JACS. 2013; 135 :9287–90. - 27.
Hu Y, Lin B, He P, Li Y, Huang Y, Song Y. The structural stability of and enhanced CO2 storage in MOF MIL-68 (In) under high pressures probed by FTIR spectroscopy. Chem Eur J. 2015; 21 :18739–48.