The calculated and experimental Raman spectra of the (EMI + )TFSI − ionic liquid, where EMI + is the 1-ethyl-3-methylimidazolium cation and TFSI − the bis(trifluoromethanesulfonyl)imide anion, have been investigated for a better understanding of the EMI + and TFSI − conformational isomerism as a function of temperature. Characteristic Raman lines of the planar (p) and non-planar (np) EMI + conformers are identified using the reference (EMI + )Br − salt. The anion conformer of C 2 symmetry is confirmed to be more stable than the cis (C 1 ) one by 4.5 ± 0.2 kJ mol −1 . At room temperature, the population of trans (C 2 ) anions and np cations is 75 ± 2% and 87 ± 4%, respectively. Fast cooling quenches a metastable glassy phase composed of mainly C 2 anion conformers and p cation conformers, whereas slow cooling gives a crystalline phase composed of C 1 anion conformers and of np cation conformers.

Imidazolium-based ionic liquids (ILs) involving anions of variable coordinating strength have been investigated using infrared (IR) andRaman spectroscopies, density functional theory (DFT) calculations and selective deuteration of the imidazolium CH groups. Particular emphasis has been placed on the vibrational assignments of the anion and cation internal vibrations, a prerequisite before any interpretation of spectral changes due to ion-ion interactions in these unconventional liquids. The vibrations of highly symmetric and weakly coordinating anions, such as PF 6 − , have unperturbed wavenumbers, but unexpected IR or Raman activity for some modes, showing that the anion is subjected to an anisotropic electric field. The stretching as well as the in-plane and out-of-plane bending modes of the imidazolium CH groups are anharmonic. They give broad bands that reflect a large distribution of interactions with the surrounding anions. All the bending modes are mixed with ring vibrations and the stretching modes are complicated by Fermi resonance interactions with overtones and combination of in-plane ring modes. However, the stretching vibration of the quasi-diatomic C (2) -D bond appears to be a good spectroscopic probe of the increasing cation-anion interactions when the coordinating strength of the anion increases. The broad absorption observed in the far IR with weakly coordinating anions remains practically unchanged when the acidic C (2) -H imidazolium bond is methylated and even when the imidazolium cation is substituted by tetra-alkyl ammonium or pyrrolidinium cations. It is concluded that this absorption is a general feature of any IL, coming from the relative translational and librational motions of the ions without needing to invoke C (2) -H anion hydrogen bonds.

As a probe of local structure, the vibrational properties of the 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF 4 ] ionic liquid were studied by infrared (IR), Raman spectroscopy, and ab initio calculations. The coexistence of at least four [bmim] + conformers (GG, GA, TA, and AA) at room temperature was established through unique spectral responses. The Raman modes characteristic of the two most stable [bmim] + conformers, GA and AA, according to the ab initio calculations, increase in intensity with decreasing temperature. To assess the total spectral behavior of the ionic liquid both the contributions of different [bmim] + conformers and the [bmim] + − [BF 4 ] − interactions to the vibrational spectra are discussed.

We have used resonant Raman and absorption edge spectroscopy together with first-principle calculations in order to study the structure of GeS 2 glasses (g-GeS 2 ). The glasses were prepared under different melt temperatures and cooling rates, which are shown to significantly influence the g-GeS 2 structure at the nano-scale. The combined use of Raman spectroscopy and ab initio calculations reveals the origin of the molecular level electronic structure and its connection to the interesting technological features of the g-GeS 2 . Local structure within the glasses is discussed in terms of atomic Ge n S m clusters. The band gaps computed for these clusters and their correlation to the experimental band gaps and the possible formation of band tail states are also discussed.

The effect of lithium ion coordination with the bis(oxalato)borate (BOB -) [B(C 2 O 4 ) 2 ]anion in DMSO, PEG, PPG, and d-PPG has been studied in detail by IR and Raman spectroscopy. Ab initio calculations were performed to allow a consistent analysis of the experimental data. The main features observed in the IR and Raman spectra correspond to the presence of "free", un-coordinated, BOBanions. Only with use of d-PPG as solvent a small amount of Li + ‚‚‚BOBion pairs were detected. The Raman spectra and the calculations together indicate that Li + coordinates bidentately with two end-oxygen atoms of the BOBanion. The identification of ion pairs can be used to reveal limitations of LiBOB based electrolytes. The results for LiBOB are compared with literature on other Li salts.