ROTATIONAL SPECTRA OF THE TRIFLUORO ETHANOL (TFE) -WATER CLUSTERS AND THE TFE DIMERS

Javix Thomas and Yunjie Xu

Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2G2.

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Motivation

1. Xu et al. J. Chem. Phys., 1995, 103, 9541.2. Scharge et al. Z. Phys. Chem., 2008, 222, 1407.

· TFE is an important organic solvent.

· TFE and water are often used as co-solvents in the studies of protein folding process.

· The interactions of TFE with itself and with water may play some significant roles molecular recognition of biomolcules.

The TFE monomer was extensively studied using rotational spectroscopy1 and the TFE dimer was investigated using low resolution FTIR spectroscopy.2

Related alcohols

trans conformation gauche conformation

Extra binding site

Ethanol FE

gauche conformation

TFE

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4 Conformers of TFE dimer with O-H…O H-bond

H-bond donor/acceptor: homo and het 2Insertion into intra-ring: inserted or associated X 2O lone pairs of acceptor: compact or open X 2 = 8

1.80

2.52

2.52

2.11

2.52

2.52

associated inserted

1.62

associated inserted

2.52

2.52 1.91

1.86

2.52

2.52

2.01

homo hetero

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 Confs

ΔDokJ/mol

A B CGHz

μa, μ

b, μ

c

i/hom 0 1.61147 0.43043 0.41144 -2.43, -0.13, -1.26

a/hom 2.82 1.62591 0.39955 0.38001 1.43, 2.34, -3.32

i/het 0.756 1.51552 0.44402 0.40357 3.12, 1.13, 0.25

a/het 3.226 1.83234 0.35243 0.34739 -1.28, 0.38, -3.81

MP2/6-311++g(d,p) level of theory

Properties of the four conformers of the TFE dimer

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• Searches were carried out using a chirp pulsed FTMW spectrometer.

• Final measurements were done with a cavity based FTMW spectrometer

• 0.3%~0.5% TFE (and water) in Neon or Helium backing gas ( 2~3 atm)

Experimental details

Our chirp pulsed FTMW spectrometer

G. G. Brown, B. C. Dian, K. O. Douglass, S. M. Geyer, S. T. Shipman and B. H. Pate, Rev. Sci. Inst., 2008, 79, 053103; S. Dempster, O. Sukhorukov, Q.-Y. Lei, W. Jäger, J. Chem. Phys., 2012, 137, 174303; J. Thomas, J. Yiu, J. Rebling, W. Jäger, Y. Xu, J. Phys. Chem. A., Online, Apr. 25, 2013, DOI: 10.1021/jp402552t.

Broadband spectrum of TFE+He

Assignment of the TFE dimer

10

2.82

3.23

0

1.02

ichet

ichom

achomachet

iohet

iohom

Relative energy / kJmol-1

MP2/aug-cc-pVTZ//MP2/6-311++G(d,p)

The TFE dimer versus the 2-FE dimer

X. Liu, N. Borho, Y. Xu, Eur. J. Chem. 2009, 15, 270.

0

0.76 ahet

ihom

ahomihet

Relative energy / kJmol-1

2.91 2.81

4.52

3.64

MP2/6-311++G(d,p)

6 Conformers of the TFE-water dimer

Do=0

Do=10.9 Do=21.6

Do=22.3

MP2/6-311++G(d,p), ZPE corrected: kJ/mol

2.64

1.872.38

2.06

2.55 2.172.55

2.55

2.27

1.77

1.70

Do=9.0 Do=16.7

Broadband spectrum of TFE+water+He

TFE+water+He TFE+He

Assignment of the TFE-water spectrumSimulated spectrum of the TFE-water

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Semirigid rotor fits of the most stable TFE-water dimer

Spec. Component 1 Component 12Const.

A 3.5428110(9) 3.542896(1) B 1.5504968(2) 1.5504926(2) C 1.3583053(2) 1.3582814(2)

DJ 0.1299(2)E-05 0.1298(3)E-05 DJK -0.39(2)E-06 -0.37(2)E-06 DK 0.24(2)E-05 0.24(2)E-05 d1 -0.243(2)E-06 -0.241(2)E-06 d2 0.36(1)E-07 0.36(2)E-07

N 45 45SD 2.3 2.7

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Conclusion and future work

** Only the most stable conformer of the TFE dimer was identified, in contrast to the related ethanol and 2- fluoroethanol cases.

** Some unassigned lines may be attributed to the TFE trimer and perhaps even the TFE tetramer.

** Many strong unassigned lines in TFE+water+He are likely due to larger TFE-water clusters. Their assignments are in progress.

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Acknowledgement

Funding: UofA, NSERC, CFI, AI, Petro-Canada.

THANK YOU!

• Questions?