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Acta Physico-Chimica Sinca  2017, Vol. 33 Issue (5): 1043-1050    DOI: 10.3866/PKU.WHXB201702083
ARTICLE     
CH2 Scissor and Twist Vibrations of Liquid Polyethylene Glycol——Raman Spectra and Density Functional Theory Calculations
Lei HAN1,Li PENG1,Ling-Yun CAI1,Xu-Ming ZHENG1,Fu-Shan ZHANG2,*()
1 Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, P. R. China
2 Technology Center, Hengan Group, Jinjiang 362261, Fujian Province, P. R. China
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Abstract  

A new method is developed to effectively study the contributions of various coexisting conformations to the actual vibrational spectrum of liquid polyethylene oxide (PEO). By defining six conformations for the-(CH2CH2O)-unit, four isomers from the combinations of all the same EO conformations [(TGT)10, (TTT)10, (TTG)10, and (GTG)10] and three isomers from the combinations of other EO conformations were constructed. Their optimized geometric structures and the corresponding vibrational frequencies were then computed. The unified standards that describe the different types of the CH2 scissor and CH2 twist vibrational modes for PEO400 are proposed through the analysis of the normal modes. The relationships between the four CH2CH2-OCH2CH2 conformations and the various CH2 scissor and CH2 twist vibrational modes and frequencies are determined, and the results are used to assign the practical vibrational spectra.



Key wordsPolyethylene oxide      Conformation      Raman spectrum      Density functional theory calculation     
Received: 28 November 2016      Published: 08 February 2017
MSC2000:  O641  
Fund:  the National Natural Science Foundation of China(21473163);National Basic Research Program of China (973)(2013CB834604)
Corresponding Authors: Fu-Shan ZHANG     E-mail: zxm@zstu.edu.cn
Cite this article:

Lei HAN,Li PENG,Ling-Yun CAI,Xu-Ming ZHENG,Fu-Shan ZHANG. CH2 Scissor and Twist Vibrations of Liquid Polyethylene Glycol——Raman Spectra and Density Functional Theory Calculations. Acta Physico-Chimica Sinca, 2017, 33(5): 1043-1050.

URL:

http://www.whxb.pku.edu.cn/10.3866/PKU.WHXB201702083     OR     http://www.whxb.pku.edu.cn/Y2017/V33/I5/1043

Fig 1 Six conformations of the-[CH2CH2O]-unit
Conformation -E/hatree Zero-point vibrational energy/(kJ?mol-1) ΔE/(kJ?mol-1)a Dihedral angles/(°)b
gas phase (TTT)10 1614.7124 1683.9310 0.0 180/180/180
(TGT)10 1614.7069 1684.3496 14.65 (14.65) 177/72/177
(TTG)10 1614.6948 1687.6991 46.47 (50.24) 177/177/82
(GTG)10 1614.6836 1689.3738 75.78 (80.81) 92/177/92
(GTT-TTT-TTG-TTT)2-GTT-TTT 1614.7045 1686.4430 20.93 (23.45)
(GTT)2(TTG)2(GTT)2(TTG)2(GTT)2 1614.6964 1687.6991 41.87 (45.22)
(GTG)6(GTT)2(GTG)2 1614.6862 1688.9551 69.08 (74.11)
water solvent model (TGT)10 1614.7431 1685.1870 0 180/69/180
(TTT)10 1614.7325 1681.4189 27.63 (23.86) 180/180/180
(TTG)10 1614.7179 1686.4430 66.15 (67.41) 175/175/81
(GTG)10 1614.7106 1689.3738 85.41 (89.60) 91/179/91
(GTT-TTT-TTG-TTT)2-GTT-TTT 1614.7259 1684.3496 45.22 (44.80)
(GTT)2(TTG)2(GTT)2(TTG)2(GTT)2 1614.7192 1686.0244 62.80 (63.64)
(GTG)6(GTT)2(GTG)2 1614.7121 1688.5364 81.64 (85.41)
Table 1 Seven geometric conformations of PEO400 and the corresponding dihedral angles computed using B3LYP/6-31G (d) level of theory
Fig 2 Seven conformational structures of PEO400 obtained using the PCM solvent model atB3LYP/6-31G (d) level of theory
Fig 3 FT-IR (top) and Raman (middle) spectra of neatliquid PEO400, and Raman spectrum (bottom) ofn(PEO400) : n(H2O) = 1 : 1 sample Raman excitation wavelength = 488 nm
Fig 4 (a) Comparison between the experimental Raman spectrum of sample and the calculated TGT Raman spectrum using B3LYP/6-31G (d) level of theory and (b) linear regression fitting between main experimental Raman frequencies andthe corresponding calculated ones Raman excitation wavelength = 488 nm
Calc. Raman FT-IR Description
a(Raman/IR) b neat liquid water neat liquid
v1 1541(139/0.1) 1481 1468 s 1468 s 1471 w CH2 scissor
v2 1522(21.3/0.9) 1463 1446 m sh 1446 m sh 1456 w
v3 1520(12.5/43.6) 1456
v4 1488(31.6/0.1) 1431 CH2 wag
v5 1450(22.6/0.7) 1393
v6 1437(6.7/40.7) 1383 CH2 wag + H-C-O-H bend
v7 1424(10.1/3.4) 1370 1352m CH2 wag
v8 1408(15.6/17.8) 1355
v9 1389(0.1/370) 1337
v10 1329(42.2/46.0) 1280 1296 m sh 1296 m sh 1298w CH2 twist + H-C-O-H bend
v11 1320(171/2.9) 1272 1279 s 1280 s 1250m CH2 twist
v12 1277(26.8/82.6) 1231
v13 1267(55.5/0.2) 1221 1238m 1242m
v14 1250(9.9/28.5) 1206 CH2 twist + H-C-O-H bend
v15 1235(8.3/28.7) 1191
v16 1172(14.3/147) 1131 1130s 1131 m C-O-C asym. stretch
v17 1153(21.1/453) 1113 1109 s
v18 1135(0.04/889) 1096
v19 1111(1.0/39.9) 1073 CH2 rock + C-O stretch
v20 1106(7.4/28.5) 1068
v21 1100(1.8/68.4) 1063
v22 1088(13.8/156) 1051 1054m 1059m 951 m C-O-C sym. stretch
v23 1072(5.4/57.2) 1036 1036m 1034m CH2 rock + H-C-O-H bend
v24 978(0.01/205) 947 C-C stretch
v25 969(1.4/27.1) 938
v26 964(3.4/53.4) 934
v27 952(0.4/42.2) 922
v28 942(7.5/13.5) 913
v29 912(5.7/35.6) 884 H-C-O-H bend
v30 903(8.3/26.8) 876
v31 874(33.4/0.03) 848 882 s 881 m 887 w CH2 rock
v32 859(29.4/102) 834 831 sh 840 s 841 w
v33 842(9.1/4.9) 818 805 m sh 806 m sh
Table 2 Calculated vibrational frequencies of (TGT)10 conformation using PCM solvent model andB3LYP/6-31G (d) level of theory, the experimental frequencies and the assignments of PEO400
Fig 5 Calculated Raman spectra of seven PEO400 conformations in 1300-1600 cm-1 region
Fig 6 Four CH2CH2-O-CH2CH2 conformations associated with the description of CH2 scissor and CH2 twist vibrations
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