Theoretical Characterization of Dimethyl Carbonate at Low

Subscriber access provided by - Access paid by the | University Library, UC Santa Cruz

Article

Theoretical Characterization of Dimethyl Carbonate at Low Temperatures. Rahma Boussessi, Sandra Guizani, Maria Luisa S Senent, and Nejmeddine Jaïdane J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.5b01836 • Publication Date (Web): 31 Mar 2015 Downloaded from http://pubs.acs.org on April 1, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry A is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Theoretical Characterization of Dimethyl Carbonate at Low Temperatures.

R.Boussessiab, S.Guizaniac and M.L.Senentd Departamento de Química y Física Teóricas, I. Estructura de la Materia. IEM-CSIC, Serrano 121, Madrid 28006, SPAIN. and N.Jaïdanee Laboratoire de Spectroscopie Atomique, Moléculaire et Applications-LSAMA LR01ES09, Faculté des sciences de Tunis, Université de Tunis El Manar, 2092, Tunis, Tunisie.

-------------------------------Keywords: dimethyl carbonate, spectrum, torsion, rotation, vibrations a) Permanent address: Laboratoire de Spectroscopie Atomique, Moléculaire et ApplicationsLSAMA LR01ES09, Faculté des sciences de Tunis, Université de Tunis El Manar, 2092, Tunisie b) E_mail: [email protected] c) E_mail : [email protected] d) E_mail: [email protected]; author for correspondence; Tf: +34915616800 e) E-mail: [email protected]

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 34

ABSTRACT

Highly correlated ab initio methods (CCSD(T) and RCCSD(T)-F12) are employed for the spectroscopic characterization of gas-phase of dimethyl carbonate (DMC) at low temperatures. DMC, a relevant molecule for atmospheric and astrochemical studies, shows only two conformers, cis-cis and trans-cis, respectively, of C2V and Cs symmetries. cis-cis-DMC represents the most stable form.

Using

RCCSD(T)-F12 theory, the two sets of equilibrium rotational constants have been computed to be Ae =10493.15 MHz, Be =2399.22 MHz, and Ce =2001.78 MHz (cis-cis) and to be Ae =6585.16 MHz, Be =3009.04 MHz, and Ce =2120.36 MHz (trans-cis). Centrifugal distortions constants and anharmonic frequencies for all the vibrational modes are provided. Fermi displacements are predicted. The minimum energy pathway for the cis-cis → trans-cis interconversion process is restricted by a barrier of ~3500 cm-1. DMC displays internal rotation of two methyl groups. If the non-rigidity is considered, the molecule can be classified in the G36 (cis-cis) and the G18 (trans-cis) symmetry groups. For cis-cis-DMC, both internal tops are equivalent and the torsional motions are restricted by V3 potential energy barriers of 384.7 cm-1. trans-cis-DMC shows two different V3 barriers of 631.53 cm-1 and 382.6 cm-1.

The

far

infrared

spectra linked to the torsional motion of both conformers are analyzed independently using a variational procedure and a two-dimensional flexible model. In cis-cis-DMC, the ground vibrational state splits in nine components one non-degenerate (0.000 cm-1 (A1), and four quadruply degenerate, 0.012 cm-1 (G) and four doubly-degenerate 0.024 cm-1 (E1 and E3)). The methyl torsional fundamentals are obtained to lie at 140.274 cm-1 (ν15) and 132.564 cm-1 (ν30).


Page 3 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION

At room temperature, dimethyl carbonate (DMC, CH3O-CO-OCH3, dimethyl ester) is a liquid (melting point = 2-4ºC and boiling point = 90ºC) usually employed as a methylating agent and as a solvent. It is considered to be a green reagent and it has been exempted from classification as a volatile organic compound (VOC).1 Since DMC shows very high oxygen content, it has been suggested as potential oxygenated fuel additive.2 This application has motivated studies of its environmental impact when it is released into the atmosphere where it develops a rich green atmospheric chemistry.2 The structure DMC has attracted special attention because the molecule presents various conformers that intertransform through internal rotation.3 It has also attracted interest because DMC shares the empirical formula of C3H6O3 with a large list of isomers which have been the object of previous microwave spectroscopy studies4 motivated by the astrophysical search in the space where isomerism is a frequent fact.5 Their relative abundances in extraterrestrial sources have been discussed in terms of relative stability and on the basis of molecular properties (i.e. the collisional parameters) that can be keys of the detectability.5,6. Not necessarily the most abundant isomeric forms in astrophysical sources are the more stable ones. For example, among the C2H4O2 compounds, methyl formate is more abundant in the interstellar medium than acetic acid. For C3H6O3 molecules, nothing can be said because only dihydroxyacetone has been astrophysically discovered.7,8 The facts that only lactic acid and DMC are commercialy available and some species show very low dipole moment, can explain why these species have not been detected.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Recently, Lovas et al.

4

have determined the binding energies of thirteen

C3H6O3 isomers. In this ranking of stabilities, DMC is placed in the fourth position with a relative energy of ~4500 cm-1 with respect to the most stable one, the lactic acid.4 Furthermore, DMC shows at least two conformers cis-cis and trans-cis and a third neartrans-near-trans stable structure has been postulated3. Recently, the microwave spectrum of the cis-cis form was measured by Lovas et al. 4 over the frequency range of 8.4 - 25.3 GHz and over 227 -350 GHz. The analysis and assignments were accomplished with the Xiam and Erham programs developed for systems with two identical methyl tops.9,10 The dipole moment has been evaluated to be 0.293(3) debyes.4 Measurements of the Raman spectrum of DMC started very early.11,12 In 1966, Collingwood et al recorded the infrared spectrum between 4000 and 400 cm-1.13 Later, in 1974, Katon and Cohen reported studies in liquid and solid phases.14 In 1999, Bohets and van der Veken have analysed and assigned both infrared and Raman spectra in vapour, and in amorphous and crystalline solid phases between 4000-50 cm-1, respectively on the basis of MP2/6-31G(d,p) and DFT/6-31G(d,p) ab initio calculations3. Other previous theoretical studies are also available.15,16 The harmonic frequencies for all the vibrational modes were determined at different levels of theory by Sun et al.15. In this new paper, we provide accurate theoretical molecular properties that we expect can help future experimental assignments of spectra motivated by the search of new molecules in astrophysical sources. For this purpose, we use state-of-the art ab initio methods to focus on the spectroscopic characterization of DMC at low temperatures. Under these conditions, the lower torsional energy levels can be populated. DMC displays a complex far infrared spectrum because four internal


Page 4 of 34

Page 5 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


rotations, the C-OCH3 torsions (denoted by α1 and α2, in this paper) and the two methyl group torsions (denoted by θ1 and θ2, in this paper) are responsible for the non-rigid properties. The α1 and α2 torsions cause the conformer intertransformation, whereas θ1 and θ2, transform equivalent minima. For each conformer, we analyse the far infrared spectra (FIR and Raman) using a two-dimensional variational model for which independent coordinates are θ1 and θ2 . The study is applied to the cis-cis and trans-cis conformers independently, on the basis that the energy barrier between both structures (~3500 cm-1) is sufficiently high to justify this theoretical treatment. Spectroscopic parameters obtained using second order perturbation theory, are also provided for all the vibrational modes and they are used to help the variational calculations.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

RESULTS AND DISCUSSION

Computational details The structural parameters of the two DMC conformers and the equilibrium rotational constants have been computed using the explicitly correlated coupled-cluster method CCSD(T)-F12b,17,18 implemented in MOLPRO (2012).19 The default options were selected. The atomic orbitals were described by the cc-pVTZ-F12 basis set of Peterson et al.20 (denoted in this paper by VTZ-F12) in connection with the corresponding basis sets 21 for the density fitting and the resolutions of the identity. The rotational constants were enhanced adding a core-valence correlation correction determined with CCSD(T) (coupled-cluster theory with singles and doubles substitutions, augmented by a perturbative treatment of triple excitations) 22 and the ccpCVTZ basis set.23,24 The rotational parameters (rotational constants at the vibrational levels as well as, the centrifugal distortion constants) and the harmonic and anharmonic frequencies for all the vibrational modes were calculated using vibrational second order perturbation theory (VPT2) as implemented in Gaussian 09.25 To limit computational expense, which is significant given the molecular size (DMC contains six heavy atoms and six hydrogen atoms) different levels of theory were combined. For the first order properties, such as the rotational constants or the harmonic fundamentals, very accurate methods were employed. However, anharmonic effects were computed at lower levels of theory. Thus, anharmonic quadratic, cubic and quartic force field was obtained with MöllerPlesset theory (MP2) in connection with the cc-pVTZ correlation-consistent basis set (denoted in this paper by VTZ).26


Page 6 of 34

Page 7 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The torsional parameters and the torsional energy levels were determined using a variational procedure for solving a vibrational Hamiltonian of reduced dimensionality. For this purpose, we employed our code ENEDIM.27 All the kinetic and potential parameters of the two-dimensional Hamiltonian were computed using a set of MP2 geometries. Single point CCSD(T) calculations were performed on the MP2 geometries to obtain refined potential parameters. The augmented correlation-consistent basis set aug-cc-pVTZ (denoted in this paper by AVTZ), was used.28

Equilibrium geometries After an exhaustive search of equilibrium structures using MP2/AVTZ, we concluded that DMC shows only two planar conformers of C2V and Cs symmetry, respectively (see Figures 1 and 2). In this paper, we refer to them as cis-cis-DMC and trans-cis-DMC. cis-cis-DMC is the most stable conformer. If the methyl group internal rotational rotation is considered, the corresponding Molecular Symmetry Groups (MSG) are the G36 and G18. The structural parameters are shown in Table 1, as well as, the rotational constants. The search for more minimum energy geometries (i.e. neartrans-near-trans 3) has been unproductive. We found a structure with imaginary frequencies. Figure 1 shows the minimum energy pathway for the cis-cis → trans-cis conversion process which is restricted by a barrier of 3501 cm-1 when CCSD(T) theory is employed. At the CCSD(T)-F12 level of theory, the trans-cis-DMC lies 1091.5 cm-1 over the cis-cis-form (see Table 1). As was expected, the process carries out a significant change of the dipole moment (from 0.3498 D to 3.9212 D). However, with the exceptions of three angles, O3C1O2, C4O2C1 and O6C1O2, the process occurs



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 34

without significant changes in the structural parameters. The two methyl groups display a slightly distorted C3v structure. In Table 1 displays the equilibrium and the ground vibrational state rotational constants. The last are compared with previous experimental data derived from microwave spectroscopy.4 cis-cis-DMC is a near prolate top (κ ~ -0.91) and trans-cisDMC is a clear asymmetric rotor (κ ~ -0.60). The equilibrium parameters of the cis-cis and trans-cis forms were computed to be Ae =10493.15 MHz, Be =2399.22 MHz, and Ce =2001.78 MHz and to be Ae =6585.16 MHz, Be =3009.04 MHz, and Ce =2120.36 MHz, respectively. The ground vibrational state rotational constants were obtained using the equation: B0= Be + ∆Becore + ∆Bvib Here, ∆Becore, regards the core-valence-electron correlation effect on the equilibrium parameters, It was computed at the CCSD(T)-cc-pCVTZ level of theory as the difference between Be (CV), (calculated correlating both core and valence electrons) and Be(V) (calculated correlating just the valence electrons).

∆Bvib represents the

vibrational contribution to the rotational constants derived from the VPT2 αri vibrationrotation interaction parameters determined using the MP2 cubic force field (see below). The resulting corrections are:

cis-cis trans-cis

∆Avib -94.61 -58.35

∆Aecore 33.95 17.91

∆Bvib -25.46 -34.48

∆Becore 5.32 6.72

∆Cvib -20.47 -22.74

∆Cecore 4.81 5.05

The ground vibrational state rotational constants of most stable cis-cis form has been estimated to be A0 =10432.29 MHz, B0 =2379.08 MHz, and C0 =1986.12 MHz in a good agreement with the experimental parameters of Ref.[4] (A0 =10411.707 (5)


Page 9 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


MHz, B0 = 2371.5263 (9) MHz, and C0 = 1980.2513 (9) MHz). They are shown in Table 1.

Full-dimensional anharmonic analysis The anharmonic force field has been computed at the MP2/VTZ level of theory. In Table 2, VPT2 harmonic and anharmonic frequencies are compared with the experimental infrared and Raman transitions recently measured by Bohets and van der Veken.3 The experimental band centers which are emphasized in bold, correspond to the Raman transitions3. The calculated values have been tentatively assigned to local modes (s=stretching, b=bending and t=torsions) and have been classified following the representation of the C2v and Cs groups. Especially tricky is the correlation of normal torsional modes and local modes. For the low frequency modes, this correlation is almost impracticable because the α coordinates (C-OCH3 torsions) are strongly coupled with the θ coordinates (methyl torsions) in the normal coordinates. The experimental sample 3 contains a mixture of the two DMC conformers. The main observed bands were assigned to the most stable one 3. Some of the unassigned transitions observed at (1105 cm-1, 1047 cm-1, 633 cm-1 and 578 cm-1) were correlated to the second conformer. On the basis of the agreement between our anharmonic values and the experimental data for the previously assigned bands, we propose new assignments of the unclassified trans-cis transitions to the fundamentals band centers ν13, ν14, ν16 and ν17.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Focusing on the torsional two-dimensional analysis (see below), one of the most beneficial uses of the VPT2 theory is the prediction of Fermi interactions. Calculated bands for which the expected Fermi displacements are larger than 5 cm-1, are emphasized in bold. This occurs with ν2(a1) and the ν18(b2) methyl stretching fundamentals of the cis-cis form. In the case of the trans-cis form, three fundamental ν3(a’) , ν4(a’) and ν18(a’) are also displaced. Strong Fermi interactions among the torsional modes and the remaining vibrations are not predicted (see Table 3). This validates the two dimensional model employed below. Few possible displacements are obtained, i.e. the combination levels ν15 + ν29 and ν15 + ν30 levels interact with the COC bending fundamental (ν25). This effect displaces ~10 cm-1 the torsional combination bands, in the cis-cis conformer. In the case of the trans-cis-conformer, the overtone 2ν28 (methyl torsion) is strongly coupled with the COC bending fundamental (ν18). The corresponding torsional band can be displaced an amount of 13 cm-1 to the lower frequencies. Table 3 displays rotational constants in the torsional fundamentals and centrifugal distortion constants.

Variational torsional analysis The methyl torsional energy levels were determined variationally assuming very small, almost negligible, interactions between the two methyl torsional modes and the remaining vibrations. Under these conditions, it is possible to define the following torsional Hamiltonian for J=0:29,30

Ĥ , = − , + , 1


Page 10 of 34

Page 11 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Where the independent coordinates θ1 and θ2 are identified with the two CH3 torsions (see Figure 1). These two coordinates are defined as a function of three dihedral angles:31

θ1 = (H7C4O2C1+ H8C4O2C1+ H9C4O2C1)/3- π θ2 = (H10C5O3C1+ H11C5O3C1+ H12C5O3C1)/3-π

(2)

Bθiθj and Veff(θ1,θ2) represent the kinetic energy parameters and the effective potential energy surface. This last can be defined as the sum of three terms:

, = , + , +

!"# , 3

where V(θ1, θ2), V’(θ1, θ2) and VZPVE(θ1, θ2) are the potential energy surface, the pseudopotential and the zero point vibrational energy correction, respectively.29,30,32 One aspect that is important to discuss is the validity of the 2-dimensional model for DMC because a treatment in four-dimensions appears to be more precise given the strong coupling between α and θ coordinates. All the out of plane bending coordinates involving the O-CH3 groups contribute to the torsional normal coordinates. In addition, in trans-cis-DMC, the 2ν29 overtone interacts with the COC bending fundamental (see Table 3). Although a 4D-model (or a 5D model) could provide more accurate frequencies, it is extremely expensive from the computational point of view. Furthermore, the assignments of previous experimental microwave studies have been performed using effective Hamiltonian for two-identical tops. To our knowledge, effective Hamiltonians depending on many vibrational variables are not contemplated for future rotational assignments. To avoid large computational effort and to consider these interactions 11 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

partially, we have employed a flexible two-dimensional model where the α coordinates and the remaining internal coordinates are allowed to be relaxed during the CH3 internal rotation. The potential energy surface is calculated from the energies of 7 and 10 conformations for selected values of the H7C4O2C1 and H10C5O3C1 dihedral angles. A set of 3Na-8 internal coordinates (Na=number of atoms) are allowed to be relaxed. For all the structures, the zero point vibrational energy is corrected within the harmonic approximation: %

!"#

)*+,

, =

')

&' 4 2

To obtain the effective potential energy surfaces, we combine different levels of ab initio calculations. The geometries are optimized using MP2/VTZ; the energies are obtained in CCSD(T)/AVTZ single point calculations and zero point vibrational energy correction is determined with MP2/VTZ. For both conformers, the effective surfaces are determined by fitting the effective energies to the double Fourier series transforming as the totally symmetric representation of the G36 and G18 Molecular Symmetry Groups. Thus, for cis-cis-DMC:

Veff(θ1,θ2)= 415.378 - 192.83 (cos3θ1 + cos3θ2) + 1.178 cos3θ1 cos3θ2 - 14.582 (cos6θ1 + cos6θ2) - 0.720 (cos6θ1 cos3θ2 + cos3θ1 cos3θ2) - 0.292 cos6θ1 cos6θ2 - 2.166 sin3θ1 sin3θ2

and for trans-cis-DMC:


Page 12 of 34

Page 13 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Veff(θ1,θ2) = 541.588 - 323.084 cos3θ1 - 198.679 cos3θ2 + 6.958 cos3θ1 cos3θ2 - 12.012 cos6θ1 -16.712 cos6θ2 + 0.431 cos6θ1 cos3θ2 + 0.361 cos3θ1 cos3θ2 + 1.151 cos6θ1 cos6θ2 + 1.207 sin3θ1 sin3θ2

From this effective potential energy surfaces, the energy barriers and potential parameters shown in Table 4, can be derived. This table also shows the kinetic energy parameters calculated with the code ENEDIM

27

from the optimized geometries of the

conformers. The effective rotation barriers, V3, of the two equivalent methyl torsions of cis-cis-DMC have been evaluated to be 384.7 cm-1. They have found to be 631.53 cm-1 and 382.6 cm-1 for trans-cis-DMC where the two tops are not equivalent. Onedimensional cuts of the surfaces are shown in Figure 3. The cis-barriers are of the same order of magnitude as for acetone (367.07 cm-1)

33

and for methanol (377.94 cm-1).34

Table 4 shows also the difference of energies E(60º,60º) - E(60º,0º) - E(0º,60º) that can be understood as a measure of the two-methyl group interactions between the two methyl groups. This difference is very small compared to other molecules such as acetone

33

or dimethyl-ether.35,36 The more significant interaction terms of the surfaces

cos3θ1 cos3θ2 and sin3θ1 sin3θ2 present expansion coefficients almost negligible if they are compared to the heights of the torsional barriers. The torsional energy levels of both conformers are shown in Table 5. The first columns are devoted to the calculations performed using V(θ1,θ2), and the second columns, to those performed with Veff(θ1,θ2). Both groups of energies are denoted by E and Eeff. The energy levels are classified following the representations of the G36 and the G18 MSG and the vibrational quanta. cis-cis-DMC presents two methyl torsional modes ν15(b1) and ν30(a2), one active in infrared and the second one, inactive. In the case of trans-cis-DMC, both modes are infrared active. The bands assigned to ν28(a”) are



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

expected to be more intense than those of ν27(a”). Since the 2D-potential energy surface shows nine minima, each level splits into nine components. For cis-cis-DMC, the sublevels are one non-degenerate (Ai, i=1,2,3,4), two two-degenerate (Ei and Ej, i=1,2; j=3,4) ) and one four times degenerate (G). The G components of the two fundamentals, which are expected to be the prominent subcomponents, are calculated to lie at 140.274 cm-1 (ν15) and 132.564 cm-1 (ν30) with the isotopically corrected potential. The (0, 0) ground state subcomponents are found to be 0.000 cm-1 (A1), 0.012 cm-1 (G) and 0.024 cm-1 (E1 and E3). The trans-cis levels split into one doubly-degenerate sublevel (Ai; i=1, 2), and four quadruply-degenerate (Ej; i=1, 2, 3, 4). In this case the two fundamentals are found at 170.358 cm-1 (ν28) and 136.105 cm-1 (ν27) and the (0, 0) sublevels at 0.000 cm-1 (A1), 0.001 cm-1 (E1) and 0.0011 cm-1 (E2, E3 and E4). The energy differences between subcomponents are smaller in the trans-cis-form where one of the barriers is double higher than is cis-cis-DMC. Unfortunately, there are not experimental data available to compare our results. To our knowledge, the unique observation in this spectrum region are from Bohets and Veken,3 who have observed un assigned Q branches of Type C bands at 126 cm-1 and 118 cm-1. It seems reasonable to assign them to torsional out-of-plane modes. What is not possible to clarify if they have be assigned to methyl group torsion or to the CO bond torsions. Furthermore, some both types of torsions are participating in all the torsional normal modes, and this makes difficult the calculation of the zero point vibrational correction. Large differences between E and Eeff energies can be derived from these interactions.


Page 14 of 34

Page 15 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


When the behavior of the cis-cis and trans-cis forms is compared, it can be conclude that band centers are displaced to the large frequencies in the second conformer which show the smaller splittings.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

CONCLUSIONS The exhaustive search of equilibrium structures of DMC leads to two planar conformers of C2V and Cs symmetry. The corresponding energy difference has been calculated to be 1091.5 cm-1 and the equilibrium rotational constants to be Ae =10493.15 MHz, Be =2399.22 MHz, and Ce =2001.78 MHz (cis-cis) and to be Ae =6585.16 MHz, Be =3009.04 MHz, and Ce =2120.36 MHz (trans-cis). The ground vibrational state rotational constants of most stable cis-cis form has been estimated to be A0 =10432.29 MHz, B0 =2379.08 MHz, and C0 =1986.12 MHz. The MP2/VTZ anharmonic force field shows that the correlation of normal torsional modes and local modes is especially tricky given the coupling among all the out-of-plane vibrations of the molecule. Strong Fermi interactions among the torsional modes and the remaining vibrations are not predicted with the exception of trans-cis overtone 2ν28 (methyl torsion) which is strongly coupled with the COC bending fundamental (ν18). The effective rotation barriers, V3, of the two equivalent methyl torsions of ciscis-DMC have been evaluated to be 384.7 cm-1 and to be 631.53 cm-1 and 382.6 cm-1 for trans-cis-DMC where the two tops are not equivalent. The two fundamentals of cis-cisDMC and trans-cis-DMC are found at 140.274 cm-1 (ν15) and 132.564 cm-1 (ν30) and at 170.358 cm-1 (ν28) and 136.105 cm-1 (ν27), respectively. The energy differences between torsional splittings are smaller in the trans-cis-form where one of the barriers is double higher than is cis-cis-DMC.


Page 16 of 34

Page 17 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


FIGURE CAPTIONS FIGURE 1: CCSD(T) Pathway corresponding to the intertransformation of the two conformers of dimethyl carbonate. FIGURE 2: The equilibrium geometry of cis-cis dimethyl carbonate. Definition of the torsional coordinates. FIGURE 3: One-dimensional cuts of the 2D potential energy barriers surfaces, V3 cis-cis (θ=θ1), V3

trans-cis

(θ=θ1) and V3

trans-cis

(θ=θ2), of the cis-cis (in red) and trans-cis (in

black) conformers.

ACKNOWLEDGMENTS This research was supported by the MINECO of Spain grant FIS2013-40626-P and by the Marie Curie International Research Staff Exchange Scheme Fellowship within the 7th European Community Framework Program under grant n° PIRSES-GA2012-31754. The authors acknowledge the COST Actions CM1405 “MOLIM” and CM1401 “Our Astrochemical history”. The authors acknowledge the CTI (CSIC) and CESGA for computing facilities.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

REFERENCES (1) Tundo, P.; Selva, M. The Chemistry of Dimethyl Carbonate. Acc. Chem. Res. 2002, 35, 706–716. (2) Bilde, M.; Møgelberg, T. E.; Sehested, J.; Nielsen, O. J.; Wallington T. J.; Hurley, M. D.; Japar, S. M.; Dill, M.; Orkin V. L.; Buckley T. J. et al. Atmospheric Chemistry of Dimethyl Carbonate: Reaction with OH Radicals, UV Spectra of CH3OC(O)OCH2 and CH3OC(O)OCH2O2 Radicals, Reactions of CH3OC(O)OCH2O2 with NO and NO2, and Fate of CH3OC(O)OCH2O Radicals. J. Phys. Chem. A 1997, 101, 3514-3525. (3) Bohets, H.; Van der Veken, B. J. On the Conformational Behavior of Dimethyl Carbonate. Phys. Chem. Chem. Phys. 1999, 1, 1817-1826. (4) Lovas, F. J.; Plusquellic, D. F.; Widicus Weaver, S. L.; McGuire, B. A.; Blake G. A. Organic Compounds in the C3H6O3 Family: Microwave Spectrum of cis–cis Dimethyl Carbonate. J. Mol. Spectrosc. 2010, 264, 10–18. (5) Remijan, A. J.; Hollis, J. M.; Lovas, F. J.; Plusquellic, D. F.; Jewell, P. R. Interstellar Isomers: The Importance of Bonding Energy Differences. Astrophys. J. 2005, 632, 333–339. (6) Dumouchel, F.; Faure, A.; Lique, F. The Rotational Excitation of HCN and HNC by He: Temperature Dependence of the Collisional Rate Coefficients. Mon. Not. R. Astron. Soc. 2010, 406, 2488–2492. (7) Widicus Weaver, S. L.; Blake, G. A. 1,3-Dihydroxyacetone in Sagittarius B2(NLMH): The First Interstellar Ketose. Astrophys. J. lett. 2005, 624, 33–36. (8) Apponi, A. J.; Halfen, D. T.; Ziurys, L. M.; Hollis, J. M.; Remijan, A. J; Lovas, F. J. Investigating the Limits of Chemical Complexity in Sagittarius B2(N): A Rigorous Attempt to Confirm 1,3-Dihydroxyacetone. Astrophys. J. 2006, 643, 29-32.


Page 18 of 34

Page 19 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(9) Hartwig, H.; Dreizler, H. The Microwave Spectrum of trans-2,3-Dimethyloxirane in Torsional Excited States. Z. Naturforsch. 1996, 51a, 923–932. (10) Groner, P. Effective Rotational Hamiltonian for Molecules with Two Periodic Large-Amplitude Motions. J. Chem. Phys. 1997, 107, 4483–4498. (11) Kohlrausch, K. W. F.; Pongratz, A. Raman-Effekt und Konstitutionsprobleme, 4. Mitteil.: Carbonyl-Frequenz und Molekul-Konstitution. Ber. Dt. Chem. Ges. 1933, 66, 1355-1369. (12) Kubo, M.; Morino, Y.; Mizushima, S. Internal Rotation VIII: Molecular Structure of Carbonic Ester. Sci. Pap. Inst. Phys. Chem. Res. (Tokyo) 1937, 32, 129-131. (13) Collingwood, B.; Lee, H.; Wilmshurst, J. K. The Structures and Vibrational Spectra of Methyl Chloroformate and Dimethyl Carbonate. Aust. J. Chem., 1966, 19, 1637-1649. (14) Katon, J. E.; Cohen, M. D. The Vibrational Spectra and Structure of Dimethyl Carbonate and its Conformational Behavior. Can. J. Chem. 1975, 53, 1378-1386. (15) Sun, H.; Mumby, S. J.; Maple, J.R.; Hagler, A. T. An ab Initio CFF93 All-Atom Force Field for Polycarbonates. J. Am. Chem. Soc. 1994, 116, 2978-2987. (16) Labrenz, D.; Schröer, W. Conformational Analysis of Symmetric Carbonic Acid Esters by Quantum Chemical Calculations and Dielectric Measurements. J. Mol. Struct. 1991, 249, 327-341. (17) Knizia, G.; Adler, T. B.; Werner, H.-J. Simplified CCSD (T)-F12 Methods: Theory and Benchmarks. J. Chem. Phys. 2009, 130, 054104-1-20. (18) Werner, H.-J.; Adler, T. B.; Manby, F. R. General Orbital Invariant MP2-F12 Theory. J. Chem. Phys. 2007, 126, 164102-1-18.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(19) MOLPRO, version 2012.1, a package of ab initio programs, Werner, H.-J.; Knowles, P.J.; Manby, F.R.; Schütz, M.; Celani, P.; Knizia, G.; Korona, T.; Lindh, R.; Mitrushenkov, A.; Rauhut, G.; et al. , see http://www.molpro.net (20) Peterson, K. A.; Adler, T. B.; Werner, H.-J. Systematically Convergent Basis Sets for Explicitly Correlated Wavefunctions: The atoms H, He, B–Ne, and Al–Ar. J. Chem. Phys. 2008, 128, 084102-1-12. (21) Yousaf, K. E.; Peterson, K. A. Optimized Auxiliary Basis Sets for Explicitly Correlated Methods. J. Chem. Phys. 2008, 129, 184108-1-7. (22) Raghavachari, K.; Trucks, G. W.; Pople, J. A.; Head-Gordon, M. A Fifth-Order Perturbation Comparison of Electron Correlation Theories. Chem. Phys. lett. 1989, 157, 479-483. (23) Woon, D. E.; Dunning,Jr. T. H. Gaussian Basis Sets for Use in Correlated Molecular Calculations. V. Core Valence Basis Sets for Boron Through Neon. J. Chem. Phys. 1995, 103, 4572-4585. (24) Peterson, K. A.; Dunning, Jr. T. H. Accurate Correlation Consistent Basis Sets for Molecular Core–Valence Correlation Effects: The Second Row Atoms Al–Ar, and the First Row Atoms B–Ne Revisited. J. Chem. Phys. 2002, 117, 10548-10560. (25) Gaussian 09, Revision A.02, Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A. et al. Gaussian, Inc., Wallingford CT, 2009. (26) Dunning, Jr. T. H. Gaussian Basis Sets for Use in Correlated Molecular Calculations. I. The Atoms Boron Through Neon and Hydrogen. J. Chem. Phys. 1989, 90, 1007-1023. (27) ENEDIM, “A Variational Code for Non-Rigid Molecules”, Senent, M. L. 2001; (see http://tct1.iem.csic.es/PROGRAMAS.htm, for more details).


Page 20 of 34

Page 21 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(28) Kendall, R. A.; Dunning, Jr. T. H.; Harrison, R. J. Electron Affinities of the Firstrow Atoms Revisited. Systematic Basis Sets and Wave functions. J. Chem. Phys. 1992, 96, 6796-6806. (29) Senent, M. L. Determination of the Kinetic Energy Parameters of Non-Rigid Molecules. Chem. Phys. lett. 1998, 296, 299-306. (30) Senent, M. L. Ab Initio Determination of the Roto-Torsional Energy Levels of trans-1,3-Butadiene. J. Mol. Spectrosc. 1998, 191, 265-275. (31) Szalay, V.; Császár, A. G.; Senent, M. L. Symmetry Analysis of Internal Rotation J. Chem. Phys. 2002, 117, 6489-6492. (32) Császár, A. G.; Szalay, V.; Senent, M. L. Ab Initio Torsional Potential and Transition Frequencies of Acetaldehyde. J. Chem. Phys. 2004, 120, 1203-1207. (33) Smeyers, Y. G.; Senent, M. L.; Botella, V.; Moule, D. C. An ab Initio Structural and Spectroscopic Study of Acetone—An Analysis of the Far Infrared Torsional Spectra of Acetoneh6 and d6. J. Chem. Phys, 1993, 98, 2754-2767. (34) Muñoz-Caro, C.; Niño, A.; Senent, M. L. Theoretical Study of the Effect of Torsional Anharmonicity on the Thermodynamic Properties of Methanol. Chem. Phys. lett. 1997, 273, 135-140. (35) Senent, M. L.; Moule, D. C.; Smeyers, Y. G. An ab Initio and Spectroscopic Study of Dimethyl Ether: An Analysis of the Infrared and Raman Spectra. Can. J. Phys. 1995, 73, 425-431. (36) Villa, M.; Senent, M. L.; Domínguez-Gómez, R.; Álvarez-Bajo, O.; Carvajal, M. CCSD(T) Study of Dimethyl-Ether Infrared and Raman Spectra. J. Phys. Chem. A. 2011, 115, 13573-13580.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 34

TABLE 1: CCSD(T)-F12/VTZ-F12 total electronic energies (E, in a.u.), relative energies (Er, in cm-1), structural coordinates (distances Å, angles inº), rotational constants (in MHz) and MP2/AVTZ dipole moment (in Debyes) of the two conformers of DMC. cis-cis C2V O2C1 1.3325 O3C1 1.3325 C4O2 1.4315 C5O3 1.4315 O6C1 1.2043 H7C4 1.088 H8C4, H9C4 1.0850 H10C5 1.0850 H11C5, H12C5 1.0850 O3C1O2 108.2 O6C1O2 125.9 O6C1O3 125.9 C4O2C1 113.4 C5O3C1 113.4 H7C4O2 105.4 H8C4O2 110.4 H9C4O2 H10C5O3 105.4 H11C5O3 110.4 H12C5O3 H7C4O2C1 180.0 H8C4O2H7 119.6 -H9C4O2H7 H10C5O3C1 180.0 H11C5O3H10 119.6 -H12C5O3H10

trans-cis

cis-cis

trans-cis

Cs 1.3335 1.3434 1.4316 1.4329 1.1982 1.0854 1.0879 1.0853 1.0876 112.2 122.8 125.1 118.6 113.3 105.1 110.9

E Er θ1 θ2 C4O2C1O3 C5O3C1O2

C2V -343.219689 0.0 0.0 0.0 180.0 180.0

Cs -343.214716 1091.5 0.0 0.0 0.0 180.0

µ Ae Be Ce A0 B0 C0

Calc. Exp. [4] 0.3498 10493.15 2399.22 2001.78 10432.29 10411.707 (5) 2379.08 2371.5263 (9) 1986.12 1980.2513 (9)

Calc. 3.9212 6585.16 3009.04 2120.36 6544.72 2981.28 2102.67

105.5 110.2 180.0 119.0 180.0 119.0


Page 23 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TABLE 2: Harmonic and anharmonic fundamental frequencies (ω and ν , in cm-1) of DMC calculated with MP2/VTZ cis-cis Assign. ν1

a1

CH3 s

ν2

CH3 s

ν3

C=O s

ν4 ν5 ν6

CH3 b CH3 b CH3 b

ν7

CH3-O s

ν8

CO2 s

ν9

CO2 b

ν10

COC b

ν11 ν12 ν13 ν14 ν15 ν16 ν17

b1

b2

CH3 s CH3 b CH3 b CO3 b CH3 t CO t CH3 s

ν18

CH3 s

ν19 ν20 ν21 ν22 ν23 ν24 ν25 ν26 ν27 ν28 ν29 ν30

CH3 b CH3 b CO2 s CH3 b CH3-O s O=CO2 b C-O-C b CH3 s CH3 b CH3 b OC t CH3 t

a2

ω

trans-cis νa

Expb

3220 3082 3037 3036 3095 3031 2968 2970 1812 1784 1774 1774 1524 1495 1476 1442 1435 1242 1214 1210 1215 1159 1126 1130 1130 936 917 921 921 521 514 516 517 246 241 244 250 3189 3050 3006 1509 1468 1456 1198 1174 1167 812 800 798 175 169 126 132 128 118 3220 3082 3037 3036 3094 2963 2968 2970 1522 1494 1502 1464 1456 1334 1293 1293 1218 1192 1020 990 990 703 694 693 359 356 373 3189 3050 3006 1508 1467 1456 1195 1171 212 207 158 154 -

Assign. a’

a’’

Expc

ω

ν

CH3 s

3219

3081

CH3 s

3213

3075

CH3 s

3097

3016

CH3 s C=O s CH3 b

3094 1838 1525

3039 1808 1491

CH3 b

1521

1480

CH3 b

1506

1484

CH3 b

1478

1443

CO2 s

1308

1268

CH3 b CH3 b CH3-O s CH3-O s CO2 s O=CO2 b CO2 b

1227 1211 1137 1068 881 647 585

1199 1183 1106 1105 1039 1047 861 637 633 576 578

COC b

357

359

COC b CH3 b CH3 s CH3 b CH3 b CH3 b CH3 b CO3 s CH3 t CH3 t OC t OC t

253 3194 3190 1515 1506 1197 1192 799 227 185 168 138

245 3054 3052 1486 1475 1172 1167 786 218 169 167 131

a) ∆ν= Fermi displacements (emphasized in bold if ∆ν> 5 cm-1 b) Infrared frequencies of Ref. [3]; Raman transitions emphasized in bold c) Infrared frequencies of Ref. [3]; new assignments [this work]



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 34

TABLE 3: Rotational spectroscopic parameters of DMC (in MHz) calculated with MP2/VTZ. cis-cis trans-cis Κ Ae Be Ce

-0.905150 10379.8 2387.37 1989.45

κ Ae Be Ce

A0 B0 C0

10285.19 2361.91 1968.98 ν15 = 169 cm-1 10272.81 2357.30 1966.22 ν30 = 154 cm-1 10271.97 2358.38 1967.06

A0 B0 C0

A (ν15) B (ν15) C (ν15) A (ν30) B (ν30) C (ν30) ∆J ∆K ∆JK δJ δK

-0.596560 6525.35 3000.69 2110.04

6467.00 2966.21 2087.30 ν27 = 218 cm-1 A (ν27=1) 6470.63 B (ν27=1) 2955.35 C (ν27=1) 2084.43 ν28 = 169 cm-1 A (ν28=1) 6441.19 B (ν28=1) 2965.22 C (ν28=1) 2087.01

0.1876 x 10-3 0.4359 x 10-2 0.1330 x 10-2 0.3109 x 10-4 0.5422 x 10-3

∆J ∆K ∆JK δJ δK

0.4510 x 10-3 0.5585 x 10-2 -0.5872 x 10-3 0.1526 x 10-3 0.6118 x 10-3

Predicted Fermi displacments(in cm-1) ν25 (COC bending) ν15 + ν30 ν15 + ν29 (CO torsion)

357.5 → 356.0 318.2 → 311.1 372.7 → 381.3

2ν28 2ν29 (CO torsion) ν29 + ν28 ν18 (COC bending)


335.4 → 321.9 331.4 → 332.0 332.4 → 334.1 347.5 → 358.6

Page 25 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TABLE 4: Effective potential and kinetic parameters (in cm-1) of DMC calculated with CCSD(T)/AVTZ.

V3 (θ1) = E(60º,0º)-E(0º,0º) V3 (θ2) = E(0º,60º)-E(0º,0º) E(60º,60º) - E(60º,0º) - E(0º,60º) B11 B22 B12

cis-cis Cal. Exp. [4] 384.7 398.13 384.7 398.13 4.72 5.5883 5.5883 -0.2801


trans-cis Calc. 631.5 382.6 7.82 5.4290 5.4956 -0.1153


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 34

TABLE 5: Low torsional energy levels (in cm-1) of cis-cis-DMC and transcis-DMC calculated at the CCSD(T)/AVTZ level of theory. ν30 ν15 Sym. Calc. ν27 ν28 Sym. Calc. eff E E E Eeff 00 A1 0.000 0.000 00 A1 0.000 0.000 G 0.015 0.012 E1 0.001 0.001 E1 0.030 0.024 E2 0.013 0.011 E3 0.030 0.024 E3 0.013 0.011 E4 0.013 0.011 10

A3 G E2 E3

127.648 127.340 127.057 127.057

132.831 132.564 132.316 132.316

10

A2 E1 E2 E3 E4

132.046 132.046 131.512 131.513 131.513

136.105 136.106 135.615 135.616 135.616

01

A2 G E1 E4

135.489 135.198 134.882 134.882

140.528 140.274 139.999 140.000

01

A2 E1 E2 E3 E4

166.779 166.738 166.790 166.749 166.749

170.358 170.321 170.367 170.330 170.330

20

A1 G E1 E3

230.377 231.000 237.364 237.358

238.919 239.622 245.570 245.565

20

A1 E1 E2 E3 E4

233.558 233.558 240.376 240.377 240.377

239.865 239.866 246.526 246.527 246.527

11

A4 G E2 E4

231.793 238.401 239.258 239.262

240.554 246.716 247.627 247.631

11

A1 E1 E2 E3 E4

299.420 299.393 298.908 298.881 298.881

307.677 307.658 307.216 307.195 307.195

02

A1 G E1 E3

264.623 264.245 263.881 263.874

274.279 273.935 273.599 273.593

02

A1 E1 E2 E3 E4

314.896 315.727 306.439 306.440 306.440

320.804 321.595 312.636 312.637 312.637

158.863

163.256

ZPVE

142.507 148.771


Page 27 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2


Page 28 of 34

Page 29 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

TOC: Internal Rotation in Dimethyl Carbonate


Page 30 of 34

Page 31 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


254x190mm (96 x 96 DPI)

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

209x117mm (96 x 96 DPI)


Page 32 of 34

Page 33 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


188x179mm (96 x 96 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

207x100mm (96 x 96 DPI)


Page 34 of 34

Theoretical Characterization of Dimethyl Carbonate at Low

Recommend Documents