Raman bandshape analysis on CH and CSC stretching modes of dimethyl sulfoxide in liquid binary mixture: Comparative study with quantum-chemical calculations

Accepted Manuscript Raman bandshape analysis on C-H and CSC stretching modes of dimethyl sulfoxide in liquid binary mixture: Comparative study with quantum-chemical calculations Ganesh Upadhyay, Th. Gomti Devi PII: DOI: Reference:

S1386-1425(14)00823-3 http://dx.doi.org/10.1016/j.saa.2014.05.043 SAA 12205

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

21 November 2013 13 May 2014 14 May 2014

Please cite this article as: G. Upadhyay, Th. Gomti Devi, Raman bandshape analysis on C-H and CSC stretching modes of dimethyl sulfoxide in liquid binary mixture: Comparative study with quantum-chemical calculations, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa. 2014.05.043

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Raman bandshape analysis on C-H and CSC stretching modes of dimethyl sulfoxide in liquid binary mixture: Comparative study with quantum-chemical calculations Ganesh Upadhyay and Th. Gomti Devi* Department of Physics North-Eastern Regional Institute of Science and Technology Arunachal Pradesh-791109, India E-mail: [email protected], [email protected]

Abstract The interacting nature of dimethyl sulfoxide (DMSO) in binary mixtures has been carried out on C-H and CSC stretching modes of vibration using chloroform (CLF), chloroform-d (CLFd), acetonitrile (ACN) and acetonitrile-d3 (ACNd) solvents. Peak frequencies of both the stretching modes show blue shift with the increase in solvent concentration.

Variation of Raman bandwidth with the solvent concentration was

discussed using different mechanisms. Ab initio calculation for geometry optimization and vibrational wavenumber calculation have been performed on monomer and dimer structures of DMSO to explain the experimentally observed Raman spectra. Theoretically calculated values are found in good agreement with the experimental results. Vibrational and reorientational relaxation times have been studied corresponding to solvent concentrations to elucidate the interacting mechanisms of binary mixtures. Keywords:

Vibrational

relaxation;

bandwidth;

reorientation

time;

isotropic;

anisotropic; hydrogen bonding.

* Corresponding author. Tel: +91-360-2257401(extn.6144), fax: +91-360-2244307 E-mail:[email protected]

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1. Introduction The collective study of vibrational and reorientational motions in binary liquid mixture using polarized Raman spectroscopy is one of the best informative ways to investigate the solute-solvent interactions [1-10]. The Raman bandshape analysis of both the isotropic and anisotropic components provides detailed information about the vibrational and reorientational motions in liquids, while peak position provides information about the static interactions related to force constant, electronic structure, bonding etc. [1-7]. The isotropic Raman component is mainly influenced by homogeneous broadening that yields information about the slowly varying dynamic modulation processes which are responsible for vibrational dephasing, whereas the anisotropic Raman component shows additional reorientational broadening [1, 8]. The vibrational relaxation processes may be due to the contributions from vibrational dephasing, population relaxation and resonant energy transfer. Other factors such as dipolar, dispersion and repulsive interactions have important contribution to the Raman bandshape [8]. The frequency as well as the bandwidth of the vibrational Raman band of the reference solute is influenced by the solvent induced perturbation. Hence, a variety of analytical theoretical models have been proposed to explain the influence of solvent on the vibrational Raman bandshape in binary liquid systems [11-19]. Knapp and Fischer [1314] introduced the static and dynamical aspect of concentration fluctuations in microscopic environment for vibrational band broadening. Recently, A. K. Ojha et al. [19] developed an empirical model and found that the changes in bandwidths are influenced not only by the concentration fluctuation but also due to change in

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microviscosity at different solute and solvent concentrations. They successfully explained the variation of isotropic bandwidth of some hydrogen bonded binary systems. Musso et al. and H. Torii [8, 20- 23] used simulation methods such as Monte Carlo (MC), molecular dynamic (MD) simulations to study frequency shift and bandwidth change. Such study boosts the experimental data while interpreting the solute-solvent interaction in binary liquid mixtures. M. Musso et al. [8] studied the concentration dependence bandwidth profile of C=O stretching mode in acetone/CCl4 binary liquid mixture. Experimental results obtained using Raman spectroscopy are well supported with the results obtained by MC simulations. Dimethyl Sulfoxide (DMSO) is a molecule having wide applications in industrial, biological, medicinal and pharmaceutical sciences. DMSO, besides being used as a solvent, is a plasticizer and chemical intermediate [24]. In biological science, it is used as a cryoprotectant to prevent freezing damage of living tissue and cells during low temperature preservation. In pharmaceutical and medicinal sciences it has a great value due to its skin penetration enhancer property. Any substance which is dissolved in it can penetrate through the skin of our body. DMSO is used to decrease pain and speeds the healing of wounds, burns, and muscle and skeletal injuries. Moreover, binary mixtures of DMSO with other co-solvents are of great interest in the field of organic chemistry, chemical technology and biology [24]. Its mixture can exhibit strong nonideal mixing behaviour resulting in thermophysical properties such as viscosity, density, freezing point etc. which significantly deviate from the expected values under the assumption of ideal mixing [25].

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Various researchers studied about this molecule and acquired valuable information about the interacting phenomena of this molecule with different solvents [24-38]. H.L. Schläfer et al. [26] detected that hydrogen bonding occurs in liquid DMSO. Further, Martin et al. [27] reviewed the physical and chemical properties of liquid DMSO and estimated to the probability of hydrogen bonding and self-associations. Molecular dynamics simulations on liquid DMSO and DMSO-H2O mixture system studied by I.I. Vaisman et al. [28] observed that local order in neat DMSO is determined by both dipolar forces and molecular association and two DMSO molecules associate in antiparallel or head-to-tail fashion. Sastry et al. [30] carried out second derivative analysis of S=O stretching band in Raman spectra of DMSO in CCl4 and H2O. DMSO-CCl4 mixtures may have monomers, cyclic and linear dimers and polymers, whereas DMSO-H2O system highlights the formation of hydrogen bonded complexes in addition to smaller concentrations of monomers, dimers and polymers. T. Varnali [24] performed quantum chemical calculation to gain insight into the self association of DMSO and its interaction with different solvents. DMSO associates to itself rather than with a solvent. He found that a strong hydrogen bonded complex build up in DMSO- (H2O)2 complex, which is in good agreement with the molecular dynamics study [27]. G. Fini et al. [31] studied the isotropic and anisotropic Raman spectra of DMSO in the S=O stretching vibrational region which were explained by the presence of molecular clusters. A.S. Krauze et al. [35] studied the molecular association in DMSO-Nitromethane mixture and assigned new vibrational bands of molecules using ab initio calculations. However, limited study has been done for DMSO at different deuterated solvents. In our previous paper [2] we have studied elaborately on S=O stretching mode of DMSO

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molecule at different chemical and deuterated solvents and we obtained very interesting information about the molecular dynamics of the system. In this paper, emphasis is given on C-H and CSC stretching modes of DMSO at different chemical and deuterated solvents. A comparative study of vibrational and reorientational relaxation of C-H and CSC stretching modes of DMSO in chloroform (CLF), chloroform-d (CLFd), acetonitrile (ACN) and acetonitrile-d3 (ACNd) solvents has been displayed to probe the interacting phenomena. Ab initio calculations have been performed on monomer and dimer structures of DMSO to support the experimental results. 2. Experimental Raman spectra were recorded in the region 500-3500 cm-1 for neat DMSO as well as for different binary mixtures at various solvent concentration (volume fraction, v/v) ranging from 10 % to 90 % in CLF, CLFd, ACN and ACNd solvents separately. The volume concentration of liquid mixtures was prepared using micropipette having accuracy of ±0.005 ml. The samples were of high purity and spectroscopic graded and they are used for analysis without further purification. To record the spectra, a Renishaw RM 1000 Micro-Raman spectroscopic setup equipped with grating of 2400 grooves /mm and a peltier cooled CCD has been used. The measurements were done at 50 micron slit opening. The spectral resolution at this slit opening was 2 cm-1. The software GRAM-32 was used for data collection. The spectra were recorded with properly selected integration times (60 sec.) and accumulation numbers to minimize noise of Raman spectra. The 514.5 nm line of argon ion laser was used as an excitation source. The laser power was maintained at 50mw. The accuracy of the measurement is believed to be ±0.5 cm-1.

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2.1. Computational Work: Hartree-Fock theoretical calculation was performed to determine optimized geometries of monomer and dimer structures of Dimethyl sulfoxide with solvents using Gaussian 09W software package [39] and HF/6-31+G(d,p) method. Vibrational frequency calculations were carried out on all optimized geometries to confirm the absence of imaginary frequencies. 3. Results and discussion 3.1 Theoretical works 3.1.1 Molecular geometry: The optimized geometries for monomer and self-associated dimer structures of DMSO and their interactions with CLF and

ACN solvents using HF/6-31+G(d,p)

method are shown in Figs. (1a-f). The optimized geometrical parameters (bond lengths of selected interacting bonds) have been given in the Table1. The calculated ground state dipole moments for monomer and self-associated dimer structures are 4.42D and 0.01D. The calculated ground state energy for monomer and self-associated dimer structures are -553.21 Hartree and -1103.12 Hartree. The total energy of the self-associated dimer of DMSO is less than the sum of energies of the individual monomer. The calculated ground state energy and dipole moments at different interacting states with CLF, CLFd, ACN and ACNd solvents are given in Table1. The self-association of DMSO is formed by two intermolecular hydrogen bonds of the type S  O H  C with bond length 2.30Ǻ (Fig.1b). The DMSO molecule may interact with the CLF solvent by forming two intermolecular hydrogen bonds of the types S  O H  C and Cl  H  C having bond distances 2.06Ǻ and 3.91Ǻ respectively. Similarly, DMSO molecule may interact with

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the CLFd solvent by forming two intermolecular hydrogen bonds of the types S  O D  C and Cl  H  C . DMSO interacts with ACN through hydrogen bond of

the types S  O H  C and N  H  C with the solvent molecule at bond distances 2.32Ǻ and 2.03Ǻ respectively. A similar interacting nature of DMSO-ACNd occurs through two intermolecular hydrogen bonds of the types

S  O D  C

and

N  H  C (not shown in figure).

The theoretical peak frequencies of C-H stretching vibration of DMSO are calculated using HF/6-31+G (d, p) method. The experimental peak frequency, theoretical peak frequency, its dimer state and in interacting states with CLF, CLFd, ACN and ACNd solvents of C-H stretching vibration of DMSO are given in Table2. The theoretical peak frequencies are rescaled using the 0.9007 scaling factor [40]. The calculated peak frequency of C-H stretching vibration of DMSO monomer is found smaller than the experimental peak frequency. The peak frequencies of DMSO interacting with CLF, CLFd, ACN and ACNd solvents are found higher than the DMSO monomer. Furthermore, the C-H bond length of self-associated dimer structure of DMSO and in interacting with CLF, CLFd, ACN and ACNd solvents are found slightly smaller than that of DMSO monomer (shown in the Table1). The shortening of C-H bond length may increase the force constant of C-H bond which lead to blue shift of peak frequency. The experimental peak frequency of neat DMSO and theoretical peak frequencies of CSC stretching vibration of neat DMSO, dimer state and interacting environment with CLF, CLFd, ACN and ACNd solvents are given in Table 3. The calculated peak frequency of CSC stretching vibration of DMSO monomer is found higher than the experimental peak frequency. The peak frequencies of self-associated dimer structure of

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DMSO and in interacting states with CLF, CLFd, ACN and ACNd solvents are found higher than in DMSO monomer. The C-S bond length of DMSO monomer is 1.84Ǻ. The C-S bond length is slightly shorter in dimer state and in interacting states with CLF, CLFd, ACN and ACNd solvents (Table1). This shortening of C-S bond length may cause the strengthening of its force constant, which in turns, results the higher peak frequency of CSC stretching vibration in dimer state and in interacting environment with solvents. 3.2 Experimental results and discussion 3.2.1. C-H stretching The polarized and depolarized Raman spectra of C-H stretching mode of DMSO were recorded using CLF, CLFd, ACN and ACNd solvents as a function of solvent concentration ranging from 0% to 90% separately. The isotropic and anisotropic components of Raman spectra were determined by using the relation [41]

iso ( )  VV (v)  4 VH (v) 3

------------------ (1)

 aniso(v)  VH (v)

------------------ (2)

where IVV (ν) and IVH (ν) are Raman intensities of the polarized and depolarized Raman components measured experimentally and v is the wavenumber in cm-1. Raman spectra for C-H and CSC stretching mode of neat DMSO are shown in Fig.2. The C-H stretching vibration appears in the region of 2860-2970 cm-1. The isotropic and anisotropic peak frequencies have been found at 2910.80 cm-1 and 2911.64 cm-1 respectively. The vibrational Raman bandshapes in liquids are broadened by homogeneous and inhomogeneous mechanisms. The homogeneous line broadening is governed by Lorentzian band profile which is attributed to the short-range repulsive interactions, while

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inhomogeneous line broadening governed by Gaussian band profile which arises due to slowly varying long-range attraction forces [42]. The isotropic Raman bandshape has been analyzed by using simple curve fitting method at each solvent concentration and found to be Lorentzian at high dilution (not shown). The variation of Raman peak frequencies of isotropic ( viso ) and anisotropic ( vaniso ) components of C-H stretching vibration of DMSO were studied with solvent concentration ranging from 0% to 90% in CLF, CLFd, ACN and ACNd solvents respectively (Figs. 3 and 4). The peak frequencies of both the Raman components show signs of blue shift with the increase in solvent concentration for all the four solvents. This is in good agreement with our results of ab-initio calculation. The blue shift of peak frequency in further dilution of solute is the indication of the progressive increase of electron density about the CH carbon [43]. When CLF solvent is added to the solute DMSO, there is a chance of interaction of Cl of CLF with the H of the methyl group of DMSO. The electron of hydrogen atom is pushed toward the carbon atom by highly electronegative Cl atom of CLF due to electronic repulsion between hydrogen of solute and Cl of CLF. This leads to contraction of C-H bond of DMSO and increase its force constant. This may lead to increase of peak frequency in further dilution. The influence of H-bond to the S=O stretching vibration of DMSO is not concerned in the present study. However, the influence of hydrogen and deuterated hydrogen in interacting system is found comparable. We are getting a slight difference in peak frequencies for C-H stretching mode. We are getting similar data pattern for interacting systems with ACN and ACNd solvents.

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The isotropic Raman bandwidth provides information about the vibrational relaxation mechanism which is influenced by intermolecular environment, while anisotropic Raman bandshape provides additional information about a reorientation mechanism in the system. In the study, variation of isotropic Raman bandwidth ( iso ) of C-H stretching mode of DMSO as a function of solvent concentration ranging from 0% to 90% in all four solvents are shown in Fig. 5. The data points of iso are found exponentially decrease with the increase in solvent concentration. In low solvent concentration region, the major contribution to the isotropic Raman bandshape is due to resonant energy transfer (RET) process where the microscopic local order in liquid phase permits the coupling between the vibrational states of the solute molecule through neighbouring transition dipoles. On introducing solvent molecules, the molecules diffuse towards the solute breaking its structure, thereby weakening the transition dipole-transition dipole interaction of the solute molecules. With the increase in solvent concentration, the changes incorporated in terms of spatial distribution of active molecule compounded with the diminution in the degree of microscopic local order by the solvent molecules result in the gradual fall of the contribution through RET mechanism. In brief, the decreased of data pattern is due to motional narrowing phenomena which we mentioned in previous paper [6]. The data points of aniso have shown similar pattern, which decrease in further dilution (Fig. 6). Furthermore, the band broadening of the anisotropic Raman component was found greater than that of the isotropic components. This may be due the competition of in-phase and out-phase contributions of the interacting molecules [6, 8]. The vibrational and reorientational relaxation times of any reference mode of a solute molecule serve as an efficacious probe of solute-solvent interaction. Vibrational

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relaxation originates when a molecule under investigation is close to another molecule in the environment and interacts entirely with that molecule [44]. The vibrational relaxation time of the probe molecule is influenced by the intermolecular and intramolecular environments. The relationship between vibrational and reorientational correlation times with bandwidths are given by [1]

 vib  ( c iso ) 1

-------------------- (3)

 reor  [ c (aniso  iso )]1

--------------------- (4)

where c is the velocity of light.

 vib and  reor were determined for C-H stretching mode of DMSO in all the four solvents and variation of these two parameters with the solvent concentrations ranging from 0% to 90% were plotted in Figs. 7 and 8 respectively. The data points of  vib are found to increased exponentially with the increase of solvent concentration. There are evidences of formation of self-association or dimer in DMSO [2, 42]. As the solvent molecules are added into the liquid DMSO molecule, the solvent molecules diffused into the solute environment thereby weakening its dimer structure. The solvent molecules collide elastically with the solute molecules leading to randomize the vibrational phase of the active mode. In such situation the active mode undergoes perturbation for a short time due to the competition with solvent molecules and hence its phase is retained for longer time [5]. This may result longer  vib on further dilution of the solute molecule. This is the mechanism of motional narrowing, where the bandwidth decreases and the dephasing time increases. Similar is the case for other solvent molecules also. 11

The variation of reorientation relaxation time (  reor ) of DMSO has been studied at different solvents (Fig. 8). The data points of  reor are found to increase exponentially with the increase in solvent concentration for all the four solvents. There is weakening of transition dipole-transition dipole interaction with the addition of solvent molecules in the local environment. This leads to orientation of solute molecules. However, the orientations of solute molecules were hindered with the increase of solvent concentration leading to longer  reor [6]. Moreover, breaking of self-association of solute molecules with the addition of solvents may increase the collisions between the interacting molecules. This collision may restrict the reorientational motion of the reference mode resulting increase in  reor . The data points of  reor for all solvents were compared and are found larger for ACN and ACNd solvents. This may be due to the high dielectric constant of ACN and its deuterated solvent than the other two solvents (Table 4). Comparing Figs.7 and 8, it was found that the data of  vib are much smaller than  reor , that is the reorientational relaxation time is much higher than vibrational relaxation time. 3.2.2 CSC stretching The isotropic and anisotropic Raman components of CSC stretching mode of neat DMSO is shown in Fig. 2. The CSC stretching mode of DMSO appears in the region of 580-750 cm-1 where two bands, namely symmetric and anti-symmetric bands were observed. In isotropic Raman component, symmetric stretching vibration appears at 665.61 cm-1 and anti-symmetric stretching vibration appears at 694.33 cm-1, while in anisotropic Raman component, the symmetric and anti-symmetric stretching vibrations appear at 666.61 cm-1 and 696.24 cm-1 respectively. Furthermore, symmetric band has

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higher intensity than anti-symmetric band in isotropic Raman component which is opposite to anisotropic Raman component. The spectra of CSC stretching vibration of DMSO were recorded in the region of 580-750 cm-1 at different solvent concentration ranging from 0% to 90% in CLF, CLFd, ACN and ACNd solvents. In our study we consider only symmetric CSC stretching mode, since anti-symmetric CSC stretching mode disappears at high dilution (not shown in figure). The peak frequency of CSC stretching vibration shows a blue shift with the increase of solvent concentration in all the four solvents (Figs. 9 and 10) which is of similar data pattern with the ab-initio calculations. There is chance of hydrogen bond formation with S=O of DMSO with the solvent molecules. This hydrogen bond decreases the electronegativity of oxygen and increase the electronegativity of sulfur which leads to elongation of S=O bond, thereby indirectly affecting the CSC band. There is maximum chance of shortening of CSC bond and the result is found in agreement with the theoretical calculation (Table1). The shortening of CSC bond leads to increase the force constant of CSC bond [25], thereby showing blue shift of CSC stretching vibration in further dilution of solute. The maximum frequency shift in CLF and CLFd solvents are approximately 1.69 and 1.39 cm-1 respectively, while the shift in ACN and ACNd solvents are approximately 1.79 and 1.69 cm-1 respectively (Fig. 9). The peak frequency shifts of CSC stretching bond in all the solvents are lesser as compared to C-H stretching vibration in further dilution and indirect participation of C and S atoms in the interacting environment may be one of the reasons. The variation of isotropic Raman bandwidth (Гiso) of symmetric CSC stretching mode of DMSO has been studied at different solvent concentrations ranging from 0% to 90% in

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four solvents (Fig. 11). Variation of isotropic Raman bandwidths with solvent concentration does not show similar data pattern, however, it is found decrease with the increase of solvent concentration as subchapter 3.2.1. Some data points of Гiso (Fig. 11) are found scattered in all the four solvents and it may be due to concentration fluctuation of interacting environment [11]. Hydrogen bond may be playing an important role for the DMSO-CLF interacting system. In this interacting system, there are chances of formation of two hydrogen bonds, one with Cl of CLF and other with S=O of DMSO (Fig. 1c). This may indirectly affect the CSC stretching vibration by shortening the bond, which leads to the blue shift of peak frequency. According to Knapp’s model [17], the ‘blue’ half width is more strongly affected by dilution i.e. it is decreased rapidly in further dilution due to loss of symmetry in interacting phenomena. Further, the isotropic bandshapes are found to be Lorentzian at high dilution by curve fitting method and this is an indication of rapid fluctuation of the molecules which leads to narrowing of bandwidth at high dilution. We are observing similar data pattern for other solvents also. Fig. 12 shows the variation of anisotropic Raman bandwidth (Гaniso) of CSC stretching mode of DMSO with the change of solvent concentration in all the four solvents. The Гaniso data points are also showing similar data pattern as Гiso. However, the anisotropic Raman bandwidth is found comparatively larger than isotropic Raman bandwidth. This may be due to additional contribution of orientational mechanism on anisotropic Raman bandwidth [8]. In addition to this, vibrational relaxation time (  vib ) of CSC stretching mode of DMSO was determined for all the four solvents at different solvent concentrations to get insights of the interacting environment. Variation of  vib of CSC stretching mode of DMSO in all the four solvents as a function of solvent concentration is shown in Fig. 13. The data

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points of  vib are found to exponentially increase in solvent concentration.  vib of CSC stretching vibration is influenced by intermolecular interactions of DMSO with solvent molecules although C and S atoms of DMSO are not directly interacting with solvent molecules. In DMSO, there is chance of formation of self associations. As the solvent concentration keeps on increase, the molecules of solute are confined in a potential well created by solvent molecules [6]. There may be competition among the solvent molecules to interact with fewer numbers of solute molecules and thus rapid fluctuation of molecules at this stage leads to narrower bandwidth at high dilution. Such interactions may restrict the vibrational motion of the CSC stretching mode of DMSO, resulting increase in  vib . The variation of reorientational relaxation time (  reor ) of CSC stretching mode of DMSO was studied with the solvent concentration ranging from 0% to 90% for all solvents (Fig. 14). We observed the data points of  reor increase in further dilution for all solvents. This indicates that the orientations of the solute molecules were hindered with the increase of solvent concentration leading to longer  reor , which we observed in C-H stretching vibration data. Orientational hindrance of the solute molecules in further dilution may be elucidated to the increase of collisions between the interacting molecules. This collision may restrict the reorientational motion of the reference mode, resulting increase in  reor .

4. Conclusions The solvent dependence of the Raman bandshape of C-H and CSC stretching modes of DMSO molecule has been studied in polar chemicals and their deuterated molecules. Hydrogen bond formation between DMSO and CLF, CLFd, ACN and ACNd 15

solvents has major contribution to the change in Raman bandshape. Experimental results have been compared with the quantum chemical calculations. The vibrational and reorientational

relaxation times have been studied corresponding to

solvent

concentrations. Both the relaxation times have been found to increase with the increase in solvent concentration and the results have elucidated to the interacting nature of binary mixtures in liquids. Acknowledgement The authors are thankful to Laser Raman Laboratory, Department of Physics, BHU, Varanasi for permitting to record Raman spectra.

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Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, and D. J. Fox, Gaussian, Inc., Wallingford CT, 2010. [40] J.P. Merrick, D. Moran, L. Random, J. Phys. Chem. A 111 (2007) 11683-11700 [41] K. Tanabe, Spectrochim. Acta A 40 (1984) 437-440. [42] I.S. Perelygin, J. Struct. Chem. 38 (1997) 218-226. [43] K. Mizuno. S. Imafuji, T. Ochi, T. Ohta, S. Maeda, J. Phys. Chem. B 104 (2000) 11001-11005. [44] V. Ramakrishnan, A. Sarua, M. Kuball, A.F. Abdullah, J. Raman Spectrosc. 40 (2009) 921- 935. [45] D.R. Lide, CRC Handbook of Chemistry and Physics, 82th ed., CRC Press, Boca Raton, 2001.

19

Figure Captions Fig.1

Optimized structures of DMSO (monomer), dimer of DMSO and their

interactions with CLF and ACN solvents- (1a)

DMSO monomer, (1b) dimer of DMSO, (1c) DMSO+CLF, (1d) DMSO+ACN, (1e) dimer of DMSO+CLF, and (1f) dimer of DMSO+ACN Fig. 2

Raman Spectra of C-H and CSC stretching mode of neat DMSO.

Fig. 3

Variation of isotropic Raman peak frequency  iso  associated with the C-H stretching mode of DMSO

as a function of

concentration of solvents. Fig. 4

Variation of anisotropic Raman peak frequency  aniso  associated with the C-H stretching mode of DMSO

as a function of

concentration of solvents. Fig. 5

Variation of isotropic Raman bandwidth iso  associated with the C-H stretching mode of DMSO as a function of concentration of solvents.

Fig. 6

Variation of anisotropic Raman bandwidth aniso  associated with the C-H stretching mode of DMSO as a function of concentration of solvents.

20

Fig. 7

Variation of vibrational relaxation time  vib  associated with the C-H stretching mode of DMSO as a function of concentration of solvents.

Fig. 8

Variation of reorientational relaxation time  reor  associated with the C-H stretching mode of DMSO as a function of concentration of solvents.

Fig. 9

Variation of isotropic Raman peak frequency  iso  associated with the CSC stretching mode of DMSO as a function of concentration of solvents.

Fig. 10

Variation of anisotropic Raman peak frequency  aniso  associated with the CSC stretching mode of DMSO as a function of concentration of solvents.

Fig. 11

Variation of isotropic Raman bandwidth iso  associated with the CSC stretching mode of DMSO as a function of concentration of solvents.

Fig. 12

Variation of anisotropic Raman bandwidth aniso  associated with the CSC stretching mode of DMSO as a function of concentration of solvents.

21

Fig. 13

Variation of vibrational relaxation time  vib  associated with the CSC stretching mode of DMSO as a function of concentration of solvents.

Fig. 14

Variation of reorientational relaxation time  reor  associated with the CSC stretching mode of DMSO as a function of concentration of solvents.

Table 1

The optimized geometrical parameter (selected bond length), energy and dipole moment of DMSO, dimer state and interacting with CLF, CLFd, ACN and ACNd solvents.

Table 2

The experimental (for neat DMSO) and theoretical peak frequencies of C-H stretching mode of neat DMSO, dimer state and interacting with CLF, CLFd, ACN and ACNd solvents.

Table 3

The experimental (for neat DMSO) and theoretical peak frequencies of CSC stretching mode of neat DMSO, dimer state and interacting with CLF, CLFd, ACN and ACNd solvents.

Table 4

Dielectric constant of solute and solvent molecules.

22

Figure(s)

1a

1b

2.30Ǻ

1c

3.91Ǻ

2.06Ǻ

1d

2.03Ǻ

2.32Ǻ

1e

4.52Ǻ 2.41Ǻ

2.04Ǻ

2.04Ǻ

4.53Ǻ

1f

2.31Ǻ 2.34Ǻ

2.87Ǻ

2.87Ǻ

2.31Ǻ

Fig. 1

Raman intensity / Arbitrary units --->

15000 12000

C-H stretching

C S C s tre tc h in g

Isotropic

9000

Is o tro p ic

6000

Anisotropic A n is o tro p ic

3000

Fig.2

0 600

650

700

750

W a ve n u m b e r/c m -1 -------->

2880

2920

2960

Peak frequency (iso)/cm -1--->

2920

C-H stretching DMSO: Four solvents

2918 2916 2914

CLF CLFd ACN ACNd

2912 2910 -20

0

20

40

60

80

100

Solvent Concentration (v/v) ---->

Fig. 3

Peak frequency (aniso)/cm -1--->

2922 2920

C-H stretching DMSO: Four solvents

2918

CLF CLFd ACN ACNd

2916 2914 2912 2910 -20

0

20

40

60

80

100

Solvent Concentration (v/v) ---->

Fig. 4

C-H stretching DMSO: Four solvents iso / cm -1----->

13 12 11

CLF CLFd ACN ACNd

10 9 8 -20

0

20

40

60

80

100

Solvent Concentration (v/v) ---->

Fig. 5

C-H stretching

20

DMSO: Four solvents aniso /cm -1----->

18 16 14

CLF CLFd ACN ACNd

12 10 -20

0

20

40

60

80

100

Solvent Concentration (v/v) ---->

Fig. 6

C-H stretching DMSO: Four solvents

vib/ps ----->

1.2

1.1

1.0 CLF CLFd ACN ACNd

0.9

0.8 -20

0

20

40

60

80

100

Solvent Concentration (v/v) ---->

Fig. 7

6

reor/ps ----->

5

C-H stretching DMSO: Four solvents

4 3

CLF CLFd ACN ACNd

2 1 -20

0

20

40

60

80

100

Solvent Concentration (v/v) ---->

Fig. 8

Peak frequency (iso)/cm -1--->

668

CSC stretching DMSO: Four solvents

667

CLF CLFd ACN ACNd

666

665 -20

0

20

40

60

80

100

Solvent Concentration (v/v) ---->

Fig. 9

Peak frequency (aniso)/cm -1--->

CSC stretching 667

DMSO: Four solvents

666

665 -20

CLF CLFd ACN ACNd 0

20

40

60

80

100

Solvent Concentration (v/v) ----> Fig. 10

CSC stretching DMSO: Four solvents iso /cm -1----->

14

12

10

CLF CLFd ACN ACNd

8 -20

0

20

40

60

80

100

Solvent Concentration (v/v) ---->

Fig. 11

24

CSC stretching DMSO: Four solvents

aniso /cm -1----->

21 18 15

CLF CLFd ACN ACNd

12 9 -20

0

20

40

60

80

100

Solvent Concentration (v/v) ---->

Fig. 12

1.4

CSC stretching

vib/ps ----->

DMSO : Four solvents 1.2

CLF CLFd ACN ACNd

1.0

0.8

-20

0

20

40

60

80

100

Solvent Concentration (v/v) ----> Fig. 13

4.5

reor/ps ----->

4.0

CSC stretching DMSO : Four solvents

3.5 3.0 2.5

CLF CLFd ACN ACNd

2.0 1.5 1.0 -20

0

20

40

60

80

100

Solvent Concentration (v/v) ---->

Fig. 14

1

Table1:

Mixture

Bond

Bond length (Ǻ)

Energy (Hartree)

Dipole moment (Debye)

Monomer DMSO

R (1S-3C) R (7C-9H) R (2O-14H) R (12O-9H) R (1S-3C) R (7C-9H) R (13C-14H) R (2O-12H) R (8H-14Cl) R (1S-3C) R (7C-9H) R (7C-8H) R (2O-12H) R (8H-14Cl) R (1S-3C) R (7C-9H) R (7C-8H) R (2O-15H) R (6H-12N) R (1S-3C) R (7C-9H) R (3C-6H) R (2O-15H) R (6H-12N) R (1S-3C) R (7C-9H) R (3C-6H) R (2O-14H) R (2O-27H) R (12O-9H) R (12O-21H) R (24Cl-20H) R (28Cl-6H) R (1S-3C) R (3C-6H) R (7C-9H) R (13C-14H) R (17C-20H) R (2O-14H) R (2O-27H)

1.84 1.09 2.30 2.30 1.79 1.08 1.08 2.06 3.91 1.79 1.08 1.08 2.06 3.91 1.79 1.08 1.08 2.32 2.03 1.79 1.08 1.08 2.18 2.01 1.79 1.08 1.08 2.42 2.04 2.42 2.04 4.52 4.53 1.79 1.08 1.08 1.08 1.08 2.42 2.04

-553.21

4.42

-1103.12

0.01

-1968.44

7.04

-1968.44

7.04

-683.50

3.58

-683.49

1.17

-3936.89

0.01

-3936.89

0.01

Dimer of DMSO

DMSO+CLF

DMSO+CLFd

DMSO+ACN

DMSO+ACNd

Dimer of DMSO+CLF

Dimer of DMSO+CLFd

Dimer of DMSO+ACN

Dimer of DMSO+ACNd

1The

R (12O-9H) R (12O-21H) R (24Cl-20H) R (28Cl-6H) R (1S-3C) R (3C-6H) R (7C-9H) R (13C-14H) R (17C-20H) R (2O-14H) R (2O-26H) R (12O-9H) R (12O-31H) R (27N-19H) R (22N-4H) R (1S-3C) R (3C-6H) R (7C-9H) R (13C-14H) R (17C-19H) R (2O-14H) R (2O-26H) R (12O-9H) R (12O-31H) R (27N-19H) R (22N-6H) R (1S-3C) R (3C-6H) R (7C-9H) R (13C-14H) R (17C-19H)

2.42 2.04 4.52 4.53 1.79 1.08 1.08 1.08 1.08 2.34 2.31 2.35 2.31 2.88 2.88 1.79 1.08 1.08 1.08 1.08 2.35 2.31 2.35 2.31 2.88 2.82 1.79 1.08 1.08 1.08 1.08

-1367.01

0.02

-1366.96

0.88

optimized geometrical parameter (selected bond length), energy and dipole moment of DMSO, dimer state and interacting with

CLF, CLFd, ACN and ACNd solvents.

2

Table2:

Mixture

theor (cm-1)

DMSO monomer

2884.25

Dimer of DMSO

2882.81

DMSO+CLF

2886.40

DMSO+CLFd

2886.41

DMSO+ACN

2885.08

DMSO+ACNd

2885.09

Dimer of DMSO+CLF

2886.05

Dimer of DMSO+CLFd

2886.11

Dimer of DMSO+ACN

2884.36

Dimer of DMSO+ACNd

2884.36

expt (cm-1) 2910.80 (Neat DMSO)

2 The experimental (for neat DMSO) and theoretical peak frequencies of C-H stretching mode of neat DMSO, dimer state and interacting

with CLF, CLFd, ACN and ACNd solvents.

3

Table3:

Mixture

theor (cm-1)

expt (cm-1)

DMSO monomer

670.58

665.61

Dimer of DMSO

672.04

DMSO+CLF

671.50

DMSO+CLFd

671.46

DMSO+ACN

671.18

DMSO+ACNd

671.18

Dimer of DMSO+CLF

671.85

Dimer of DMSO+CLFd

672.26

Dimer of DMSO+ACN

671.98

Dimer of DMSO+ACNd

671.97

3

The experimental (for neat DMSO) and theoretical peak frequencies of CSC stretching mode of neat DMSO, dimer state and interacting

with CLF, CLFd, ACN and ACNd solvents.

1

Table 4: [2, 45]

Molecules DMSO CLF CLFd ACN ACNd

1

Dielectric constant (  ) 46.70 4.81 4.81 37.50 37.50

dielectric constant of solute and solvent molecules.

Raman intensity/ Arbitrary units --->

C-H stretching of neat DMSO 2910.8

Isotropic

Anisotropic 2911.64

2880

2920

2960

Wavenumber/cm-1 -------->

Highlights: > Raman bands of C-H and CSC stretching modes of DMSO were studied in polar solvents.> Experimental results have been compared with the theoretically calculated results. > Variation of bandwidth and peak frequency with solvent concentration was discussed. > Vibrational and reorientation relaxation times in binary mixtures have been studied. > Solvent molecules produce a hindrance to both the relaxation times.