CH2 Rocking Modes Research Articles

Comparative study of the H and D abstraction in the H + CH3D reaction with a ten-dimensional quantum dynamics model.

The mode selectivity in the prototypical H + CH3D reaction is investigated by the initial state selected time-dependent wave packet method within a ten-dimensional quantum dynamics model. The model is a novel reduced dimensional model for the X + YCZ3 reaction, which allows the CZ3 to break C3V symmetry. The calculated reaction probabilities initially from different reactant vibrational states show that the CH3 stretching modes excitations obviously promote the H-abstraction reaction but have a slight influence on the D-abstraction reaction. In contrast, the CD stretching mode excitation significantly enhances the D-abstraction reaction. For both H- and D-abstraction reactions, the excitation of either the CH3 umbrella bending mode or the CH3 rocking mode shows a promotional effect on the reactivity, while fundamental excitation of the CH3 bending mode has a negligible effect. Impressively, the first-overtone excitation of CH3 bending mode remarkably promotes the H-abstraction reaction, resulting from the 1:2 Fermi coupling between the CH3 symmetric stretching mode and the first overtone of CH3 bending mode. In addition, translational energy is more efficient than vibrational energy in promoting the H-abstraction reaction at low energy, while vibrational energy becomes more efficient for the D-abstraction reaction.

On-Off Infrared Absorption of the S═O Vibrational Probe of Dimethyl Sulfoxide.

Dimethyl sulfoxide (DMSO), a polar solvent molecule, is used in a wide range of therapeutic and pharmacological applications. Different intermolecular interactions, such as dimerization and hydrogen bonding with water, are crucial to understanding the role of DMSO in applications. Herein, we study DMSO in various solvation environments to decipher the environment-dependent dimerization and hydrogen-bonding propensity. We use a combination of infrared spectroscopy, quantum mechanical calculations, and molecular dynamics simulations to reach our conclusions. Although DMSO can exist in a dynamic equilibrium between monomers and dimers, our results show that the relative intensity of the S═O stretch and the CH3 rocking modes is a spectroscopic indicator of the extent of DMSO dimerization in solution. The dimerization (self-association) is seen to be maximum in neat DMSO. When dissolved in different solvents, the dimerization propensity decreases with increasing solvent polarity. In the presence of a protic solvent, such as water, DMSO forms a hydrogen bond with the solvent molecules, thereby reducing the extent of dimerization. Further, we estimate the hydrogen-bond occupancy of DMSO. Our results show that DMSO predominantly exists as doubly hydrogen-bonded in water.

A Wavy-Structured Highly Stretchable Thermoelectric Generator with Stable Energy Output and Self-Rescuing Capability

A Wavy-Structured Highly Stretchable Thermoelectric Generator with Stable Energy Output and Self-Rescuing Capability

Tracking asymmetric intramolecular vibrational redistribution of nitromethane

Femtosecond time- and frequency-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy is proposed to selectively excite parent vibrational modes and detect energy flow to daughter modes in liquid nitromethane (NM, CH3NO2). The NO symmetric bending mode (δsNO2~657cm−1, symmetry: A1), CN symmetric stretching mode (νs(CN)~918cm−1, symmetry: A1), CH3 rocking mode (ρ(CH3)~1104cm−1, symmetry: B1), nitro group stretching modes (νs(NO2)~1379cm−1, symmetry: A1 and νa(NO2)~1560cm−1, symmetry: B1) of nitromethane (NM) are selectively excited in an orderly manner, vibrational energy flow to the neighboring higher ones located outside the excitation range is observed. Counterintuitive up-hill energy flow from lower frequency modes to higher ones is related to the vibrational symmetry. What's more, it is also found that up-hill intramolecular vibrational energy redistribution efficiencies decrease monotonically with the increase of the frequency differences.

Absolute Photoabsorption Cross-Sections of Methanol for Terrestrial and Astrophysical Relevance.

We investigate the methanol absorption spectrum in the range 5.5-10.8 eV to provide accurate and absolute cross-sections values. The main goal of this study is to provide a comprehensive analysis of methanol electronic-state spectroscopy by employing high-resolution vacuum ultraviolet (VUV) photoabsorption measurements together with state-of-the-art quantum chemical calculation methods. The VUV spectrum reveals several new features that are not previously reported in literature, for n > 3 in the transitions (nsσ(a') ← (2a″)) (1A' ← X̃1A') and (nsσ, npσ, npσ', ndσ ← (7a')) (1A' ← X̃1A'), and with particular relevance to vibrational progressions of the CH3 rocking mode, v11'(a″), mode in the (3pπ(a″) ← (2a″)) (21A' ← X̃1A') absorption band at 8.318 eV. The measured absolute photoabsorption cross-sections have subsequently been used to calculate the photolysis lifetime of methanol in the Earth's atmosphere from the ground level up to the limit of the stratosphere (50 km altitude). This shows that solar photolysis plays a negligible role in the removal of methanol from the lower atmosphere compared with competing sink mechanisms. Torsional potential energy scans, as a function of the internal rotation angle for the ground and first Rydberg states, have also been calculated as part of this investigation.

Novel platinum-based anticancer drug: a complete vibrational study.

The introduction of cisplatin to oncology, in the 1970s, marked the onset of the search for novel and improved metal-based anticancer drugs. Polynuclear PtII and PdII complexes with linear alkylamines as bridging ligands are a class of potential antineoplastic agents that have shown promising cytotoxicity against low-prognosis human cancers, such as metastatic breast adenocarcinoma and osteosarcoma. The present study reports an analysis of [μ-N,N'-bis(3-aminopropyl)butane-1,4-diamine-κ4N,N':N'',N''']bis[dichloridoplatinum(II)], [Pt2Cl4(C10H26N4)], denoted Pt2Spm (Spm is spermine), by vibrational spectroscopy coupled to theoretical calculations. Within the latter, the Density Functional Theory (DFT - mPW1PW/6-31G*) and Effective Core Potential (ECP - LANL2DZ) approaches were used, in order to ensure the most accurate representation of the molecule and achieve a maximum agreement with the experimental data. The solid-state geometry of Pt2Spm corresponds to Ci symmetry, displaying 132 vibrational modes. A complete assignment of the experimental vibrational profile of the system was attained through the combined application of complementary Raman, FT-IR and Inelastic Neutron Scattering (INS) techniques. INS allowed an unequivocal identification of the CH2 and NH2 rocking modes, not clearly detected by the optical techniques, while Raman measurements led to a clear discrimination of the Pt-N stretching frequencies from the two distinct Pt-N moieties within the chelate. The metal-to-metal distances calculated for the molecule under study were found to allow the establishment of effective inter- and intrastrand crosslinks with DNA. These results will hopefully help to clarify the mode of action of the compound, at the molecular level, contributing to the development of improved cisplatin-like chemotherapeutic drugs having a higher efficacy and specificity coupled to lower acquired resistance and deleterious side effects.

Propane Dehydrogenation Catalyzed by ZSM-5 Zeolites. A Mechanistic Study Based on the Selective Energy Transfer (SET) Theory

Experimentally determined activation energies of propane dehydrogenation catalyzed by ZSM-5 zeolites have been used to test the SET theory. The basis of this theory is that the catalyst system transfers vibrational energy via a resonance process to a specific vibration mode of the reacting molecule. Being excited up to a certain number of vibrational quanta the molecule is brought to reaction. By analyzing the above-mentioned activation energies we found the wave number of this “specific mode” to be 1065 cm−1. This is very close to the rocking vibration of propane (1053 cm−1). We suggest that the propane molecule reacts when excited so that the CH3 group has been forced towards a flat structure with a carbon atom hybridization that is more sp2 than sp3. Consequently there is no way for three H-atoms to bind to the carbon and one of them must leave. This is the starting point of the reaction. The isokinetic temperature of the system was found as Tiso = 727 ± 4 K. From the SET formula for Tiso when both energy-donating (ω) and energy-accepting (ν) vibrations have the same frequency, viz., Tiso = Nhcν/2R, we obtain ν = ω = 1011 ± 6 cm−1. This agrees rather well with the CH3 rocking mode (1053 cm−1) and also with asymmetric “TO4” stretching vibrations of the zeolite structure (ω).

Hydrogen bond dynamics in primary alcohols: a femtosecond infrared study.

Hydrogen-bonded liquids are excellent solvents, in part due to the highly dynamic character of the directional interaction associated with the hydrogen bond. Here we study the vibrational and reorientational dynamics of deuterated hydroxyl groups in various primary alcohols using polarization-resolved femtosecond infrared spectroscopy. We show that the relaxation of the OD stretch vibration is similar for ethanol and its higher homologues (∼0.9 ps), while it is appreciably faster for methanol (∼0.75 ps). The fast relaxation for methanol is attributed to strong coupling of the OD stretch vibration to the overtone of the CH3 rocking mode. Subsequent to excited state relaxation, the dissipation of the excess energy leads to structural relaxation of the alcohol liquid structure. We show that this relaxation of the H-bonded network depends on the alkyl chain length. We find that the anisotropy of the excitation decays by both thermal diffusion from excited OD groups to nonexcited molecules and reorientational motion. The reorientation is described well by a model employing two relaxation times that increase linearly with increasing alcohol size. The short reorientation time is assigned to the partial reorientation of molecules within the alcohol cluster, while the long reorientation times can be attributed to breaking and reforming of hydrogen bonds.

Study of the crystalline phase orientation in uniaxially stretched polypropylene by Raman spectroscopy: Validation and use of a time‐resolved measurement method

AbstractThis study proposes an experimental method to quantify the molecular orientation of the crystalline phase of isotactic polypropylene from polarized Raman spectroscopy measurements. The method is based on the intensity sensitivity of two Raman scattering bands located at 973 (C‐C stretching mode) and 998 cm−1 (CH3 rocking mode) to laser light polarization. The first part of this article is devoted to the validation of the method by comparing Raman and Wide Angle X‐ray Scattering (WAXS) results obtained on postmortem test samples uniaxially deformed at growing levels. Second, the method is applied to follow the molecular orientation in situ during a tensile test by combining a video‐controlled test machine and a Raman spectrometer. Postmortem results show a quantitative agreement between Raman and WAXS measurements. In situ results mainly evidence the ability of the Raman method to characterize molecular orientation in real‐time with less than 5 s time resolution. POLYM. ENG. SCI., 2011. ©2011 Society of Plastics Engineers .

10 μm High-resolution spectrum of trans-acrolein: Rotational analysis of the ν11, ν16, ν14 and ν16 + ν18 − ν18 bands

High-resolution Fourier transform spectra of trans-acrolein, H 2C C(H) C(H) O, have been recorded in the 10 μm region at both room and cooled temperatures on the modified Bomem DA3.002 at the National Research Council of Canada and the Bruker IFS 125HR spectrometer at the far infrared beam line of the Canadian Light Source in Saskatoon. Vibrational fundamentals analyzed so far include the ν 11, ν 16 and ν 14 bands centered at 911.3, 958.7 and 992.7 cm −1 corresponding respectively to the A′ in-plane CH 2-rocking mode, the A″ out-of-plane CH 2-wagging mode, and the A″ wagging mode highly mixed between the ⩾C H vinyl and ⩾C H formyl groups [Vibrational mode descriptions are based on Y.N. Panchenko, P. Pulay, F. Török, J. Mol. Spectrosc. 34 (1976) 283–289.] As well, the ν 16 + ν 18 − ν 18 hot band centred at 957.6 cm −1 has been analyzed, where ν 18 is the low-frequency (157.9 cm −1) A″ ⩾C C ⪕ torsional mode. The ν 11 band is a/ b type while the ν 16, ν 14 and ν 16 + ν 18 − ν 18 bands are c-type. The assigned transitions of each band have been fitted to a Watson asymmetric rotor Hamiltonian, with ground state parameters fixed to values obtained from rotational analyses in the literature. As well, a combined 3-state fit for ν 11, ν 16 and ν 14 was carried out including Coriolis and Z 1 constants which account for J and Δ K interactions. Transition dipole moments have been calculated for each of the fundamentals using the ab initio B3LYP method and 6-311++G ∗∗ basis set. For the A′ vibrational modes, we have also evaluated transition dipole a- and b-components in the principal axis system from vibrational displacements and dipole moment derivatives. Our ab initio results predict that the ν 11 in-plane CH 2 rocking mode has an a-type transition strength about three times greater than the b-type, which is consistent with our observations. Our ab initio force field analysis gives vibrational mode descriptions consistent with previously published work for all 13 A′ modes. However, for the five A″ vibrational modes, our ab initio results disagree with two of the descriptions of Panchenko et al. and three of the descriptions of Hamada et al. [Y. Hamada, Y. Nishimura, M. Tsuboi, Chem. Phys. 100 (1985) 365–375].

Rotation–torsion–vibration term-value mapping for CH 3OH: Torsion-mediated doorways and corridors for intermode population transfer

Fourier transform infrared spectra of CH 3OH from 930–1650 cm −1 have been analyzed to reveal details of the rotation–torsion–vibration energy manifold of the CO-stretching, CH 3-rocking, OH-bending and CH 3-deformation modes and their torsional combination states. Mapping of the upper-state term values as a function of the rotational quantum number J has shown the locations of numerous substate crossing resonances that give rise to J-localized spectral perturbations and substate mixing and thereby create “doorways” for collision-induced population transfer among the different modes. Other near-degenerate substates are more globally mixed over a wide range of J, corresponding to “corridors” of doorways. Where both partner substates in a doorway resonance have been identified, the perturbations have been analyzed to find estimates of the interaction matrix elements and the degree of mixing between the coupled states. Many of the resonances are between substates of differing torsional quantum number, highlighting the importance of torsion in generating the doorway channels and enhancing intermode vibrational population transfer.

Molecular Structure, Crystallinity and Morphology of Polyethylene/Polypropylene Blends Studied by Raman Mapping, Scanning Electron Microscopy, Wide Angle X-Ray Diffraction, and Differential Scanning Calorimetry

The present study is aimed at investigating the molecular structure, crystallinity, and morphology of polyethylene (PE) and polypropylene (PP) blends by using Raman mapping, scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC). In this study, three kinds of PEs, high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and metallocene polyethylene (MEPE) were used. MEPE is one of the LLDPEs but its density is very low and its melt flow index (MFI) is very high. Blends of each PE and PP with a PP content ranging from 20 to 80 wt % with an increment of 20 wt % were prepared. Raman mapping images and SEM images show that the 80/20 blends of HDPE/PP and LLDPE/PP have similar dispersibility behavior and that only the 80/20 blend of MEPE/PP shows a different behavior in this respect. For the 20/80 blends, the differences are not so large. For the Raman mapping, the intensity ratio of the two bands at 1128 and 974 cm−1 was used. The former is due to a symmetric C–C stretching mode of all-trans –(CH2)n– groups of PE while the latter is assigned to a CH3 rocking mode of PP. MEPE/PP blends yield quite different X-ray diffraction patterns compared to HDPE/PP and LLDPE/PP blends; the MEPE/PP blends show that with increasing MEPE content the crystalline size of PP become smaller. DSC curves of MEPE/PP show that the peak area changes linearly with the blending ratio and that the crystallization temperature does not change for any blend. These results mean that the density and MFI of PE influences the blend properties.

Fourier transform spectroscopy of CH 3OH: rotation–torsion–vibration structure for the CH 3-rocking and OH-bending modes

High-resolution Fourier transform spectra of CH 3OH have been investigated in the infrared region from 930 to 1450 cm −1 in order to map the torsion–rotation energy manifolds associated with the ν 7 in-plane CH 3 rock, the ν 11 out-of-plane CH 3 rock, and the ν 6 OH bend. Upper-state term values have been determined from the assigned spectral subbands, and have been fitted to power-series expansions to obtain substate origins and effective B-values for the three modes. The substate origins have been grouped into related families according to systematic trends observed in the torsion–vibration energy map, but there are substantial differences from the traditional torsional patterns. There appears to be significant torsion-mediated spectral mixing, and a variety of “forbidden” torsional combination subbands with |Δ υ t |>1 have been observed, where υ t denotes the torsional quantum number (equivalent to υ 12). For example, coupling of the ( υ 6, υ t )=(1,0) OH bend to nearby torsionally excited ( υ 7, υ t )=(1,1) CH 3-rock and ( υ 8, υ t )=(1,1) CO-stretch states introduces ( υ 6, υ t )=(1,0)←(0,1) subbands into the spectrum and makes the ν 7+ ν 12− ν 12 torsional hot band stronger than the ν 7 fundamental. The results suggest a picture of strong coupling among the OH-bending, CH 3-rocking, and CO-stretching modes that significantly modifies the traditional energy structure and raises interesting and provocative questions about the torsion–vibration identity of a number of the observed states.

Fourier transform spectra and torsion–rotation structure of the CO-stretching 2 ν8 overtone and 2 ν8– ν8 hot band of CH 3OH

The Fourier transform infrared (FTIR) spectrum of the 2 ν 8 overtone band of the CO-stretching vibrational mode of CH 3OH has been investigated in the 5-μm region at a spectral resolution of 0.0048 cm −1 (1/MOPD) and a higher pressure-path-length product than heretofore. Assignments are reported for high- K 2 ν 8 subbands in the ground state ( n=0) of the ν 12 torsion, and for 2ν 8+ν 12−ν 12 (n=1) and 2 ν 8+2 ν 12−2 ν 12 ( n=2) torsionally excited combination subbands. Upper-state υ 8=2 term values have been fitted to series expansions in powers of J( J+1) to obtain J-independent substate origins defining the torsion- K-rotation structure of the overtone state. Perturbations due to Coriolis and asymmetry resonances have been observed and characterized, as well as J-localized level-crossing resonances arising principally from interactions with the υ 7=2 overtone state of the in plane CH 3-rocking mode and the ( υ 7, υ 8)=(1,1) combination state. Differences between υ 8=2 and υ 8=1 term values have been used to generate a predicted map of the weak 2 ν 8– ν 8 CO-stretching hot band. The hot band underlies the main ν 8 fundamental in the 10-μm region, so is of significance to the determination of the fundamental line intensities. A number of the weak hot-band lines have been observed in the 10-μm FTIR spectrum.

Ab initio calculations of mode selective tunneling dynamics in CH312OH and CH313OH

A simplified formulation of the harmonic reaction path Hamiltonian (RPH) approach is used to calculate mode specific tunneling splittings and stereomutation times in CH312OH and CH313OH. The experimental torsional spectrum is very well reproduced, as well as the few known isotope shifts. The mode specific changes in tunneling splitting are investigated for the excitation of fundamentals and OH stretching overtones. Good agreement between experiment and the RPH model is obtained, except for excitations of modes which are perturbed by anharmonic resonances. The inverted tunneling splittings (E level below A) experimentally observed for the fundamental transitions of the CH-stretching modes ν2 and ν9 and of the CH-rocking mode ν11 are shown to result from a pure symmetry effect and not from a breakdown of vibrational adiabaticity. Introducing a proper geometrical phase factor but retaining the adiabatic separation of the torsional dynamics yields calculated values of Δν̃2=−3.6 cm−1, Δν̃9=−3.2 cm−1, and Δν̃11=−8.2 cm−1 that are in satisfactory agreement with experimental data. Negative tunneling splittings are also predicted for the asymmetric CH-bending modes ν4 and ν10 and the CH3-rocking mode ν7. A smooth decrease of the tunneling splitting is calculated for increasing OH stretching excitation [Δν̃(ν1)=6.2 cm−1,…,Δν̃(6ν1)=1.5 cm−1] in quantitative agreement with experiment [Δν̃(ν1)=6.3 cm−1,…,Δν̃(6ν1)=1.6 cm−1]. The effect is shown to result in about equal parts from the increase of the effective torsional barrier and the effective lengthening of the OH bond.

Spectroscopy and dynamics of methylamine. I. Rotational and vibrational structures of CH3NH2 and CH3ND2 in à states

Rovibrational structures of methylamines (CH3NH2 and CH3ND2) in predissociative à states (3s–n) are investigated using (1+1) resonant-enhanced two-photon ionization (R2PI) spectroscopy. A part of experimental results was briefly reported earlier [J. Chem. Phys. 117, 10057 (2002)], and full detailed results and analyses are given here. Spectral origins are determined to be 41 669 and 42 038 cm−1 for CH3NH2 and CH3ND2, respectively. Amino wagging and CH3 rocking modes are optically active, giving their respective fundamental frequencies of 636 (487) and 1008 (1012) cm−1 for CH3NH2 (CH3ND2). The CH3 moiety is found to rotate nearly freely about the C–N axis with respect to the amino group with an accurately determined torsional barrier of 5.0±0.5 cm−1 at the zero-point level of CH3ND2(Ã). The torsional barrier increases to 19.0±0.5 cm−1 at the v (ND2-wag)=1 level due to wagging-torsional mode coupling. Both internal and overall rotational fine structures are clearly resolved for the first few vibrational levels of CH3ND2(Ã), providing accurate values of vibrational frequencies and associated internal and overall rotational constants. Broad spectral features of the CH3NH2 excitation spectrum are unambiguously assigned by using the internal rotor Hamiltonian established in the analysis of the CH3ND2 excitation spectrum. Linewidths of spectral bands provide lifetimes of corresponding quantum states excited at particular rovibrational levels, giving, for example, ∼8.8 and ∼1.8 ps for zero-point and v (ND2-wag)=2 levels of the CH3ND2 (Ã) state, respectively. The lifetime of CH3NH2(Ã) is estimated to be much shorter, giving τ∼0.38 ps at the origin band. The large H/D isotope effect in lifetimes of excited states indicates that the primary dissociation channel is the N–H(D) bond dissociation and it proceeds via tunneling through a reaction barrier. Lifetimes are found to be mode specific, showing the experimental fact that energy deposition to a certain vibrational mode, which is perpendicular to the reaction coordinate, may modify the reaction barrier along the N–H(D) reaction coordinate. Ab initio results for structures and vibrational frequencies of methylamines at excited states are compared with the experiment.

Spectroscopy and dynamics of methylamine. II. Rotational and vibrational structures of CH3NH2 and CH3ND2 in cationic D states

Accurate and precise ionization energies of methylamines (CH3NH2 and CH3ND2) are determined to be 9.0422±0.0012 and 9.0532±0.0012 eV, respectively, by (1+1′) two-photon mass-analyzed threshold ionization (MATI) spectroscopy. From selective ionizations from specified intermediate quantum states, fundamental frequencies of amino-wagging and CH3-rocking modes of CH3NH2+ (CH3ND2+) in D0 states are determined to be 738 (573) and 1013 (1024) cm−1, respectively. The frequency of the amino wag is largely blueshifted from that of the neutral S1 state, while the CH3-rocking frequency is little shifted from that of S1. Internal rotational constants associated with the nearly free internal rotation of the top (amino group) with respect to the frame (methyl group) about the C–N axis are accurately determined, from which the geometries of methylamine ions are revealed. Barrier heights for torsional motion in CH3ND2+ are determined to be 25±5 and 34±5 cm−1 at the origin and first ND2-wagging bands, respectively. Mode-resolved spectroscopy using the MATI signal for resolving overlapped spectral features in the intermediate state is employed for clarifying the vibrational assignment of the intermediate state. An ab initio calculation at the QCISD level is carried out, giving good agreement with the experiment.

Premelting structure: Vibrational dynamics of liquid, undercooled liquid, glassy, and crystal states in methylcyclohexane and deuterated methylcyclohexane

We present the results of the Raman studies on vibrational dynamics and static properties of methylcyclohexane (MCH) and deuterated methylcyclohexane (MCH-d14) in distinct thermodynamic states ranging from normal liquid, undercooled liquid to crystal and glassy states. We have studied the low frequency Raman spectra in the range of 15–200 cm−1 and the CH2 rocking mode of MCH and MCH-d14 as a function of cooling and warming rates and temperature in the range of 10–293 K. We have identified the premelting crystal structure (crystal β) of MCH in the temperature range of 140–147 K that proceed the melting both for the glassy state and the equilibrium crystal state (crystal α) of MCH. Deuterated MCH exists only in one crystal form (crystal β) within the studied temperature range.

Low-k organosilicate films prepared by tetravinyltetramethylcyclotetrasiloxane

Low-k films with k of 2.5–2.9 were deposited under different conditions of pressures and temperatures using a plasma-enhanced chemical vapor deposition (PECVD) system. These films were prepared using a new liquid precursor, tetravinyltetramethylcyclotetrasiloxane (TVTMCTS) and H2 carrier gas. The rf power was kept as low as possible to maintain the original ring structure in the films. The as-deposited films were annealed and the dielectric and optical properties were investigated. Identification of the absorption bands in the IR spectra for as-deposited films reveals a broadband around 950–1200 cm−1 arising from the Si–O stretching mode of the ring (1065 cm−1) and chain structure (1000 cm−1), respectively; a band at 750–900 cm−1 due to Si–O bending (790 cm−1); Si–CH3 rocking mode (760 cm−1); a sharp band centered at 1260 cm−1 due to a Si–CH3 bending mode; and a broadband at 2800–3000 cm−1 due to the CH group. A comparison of the IR spectra of the PECVD film and TVTMCTS liquid reveals that vinyl vibrations (Si–CH=CH2) at 960, 1410, and 3030–3095 cm−1 for CH2 and at 1598 cm−1 for C=C present in the liquid were not detected in the CVD films. Hence C=C bonds were broken in the plasma polymerization process. As the pressure and the deposition temperature (TD) increased, the intensity of the Si–O vibration arising from the ring structure increased and decreased, respectively. Thus by tuning the pressure and TD we can control the structure of the film. There is a good correlation found between the Si–CH3 and Si–O ring intensities and k values; the increasing Si–CH3 and Si–O ring is accompanied by decreasing k. The films were thermally stable up to 400 °C annealing temperature.

Crystallization and glass formation processes in methylcyclohexane: Vibrational dynamics as a possible molecular indicator of the liquid–glass transition

We present the result of Raman studies on vibrational dynamics and static properties of the CH2 rocking mode of methylcyclohexane as a function of temperature and cooling rate. We have found that vibrational dynamics as well as the static properties are very sensitive indicators to specify phases and phase transitions at the molecular level. It was found that methylcyclohexane in the undercooled liquid phase may form distinct thermodynamic states that strongly depend on the quenching rate. We have identified the characteristic temperature T* that is quenching rate dependent which is the no-return-point between crystallization and amorphization. Below this temperature the undercooled methylcyclohexane exists in either the liquid state that is out of equilibrium and represents nonergodic behavior that leads to glass forming or in the metastable equilibrium ergodic state that leads to crystallization.