CHIRPED-PULSE FOURIER-TRANSFORM MICROWAVE SPECTROSCOPY OF THE PROTOTYPICAL C-H…π INTERACTION: THE...

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CHIRPED-PULSE FOURIER-TRANSFORM MICROWAVE SPECTROSCOPY OF THE PROTOTYPICAL C-H…π INTERACTION: THE BENZENE…ACETYLENE WEAKLY BOUND DIMER Nathan W. Ulrich, a Nathan A. Seifert, b Rachel E. Dorris, a Ashley M. Anderton, a Rebecca A. Peebles , a Brooks H. Pate, b Sean A. Peebles a a Department of Chemistry, Eastern Illinois University, 600 Lincoln Ave., Charleston, IL 61920 b University of Virginia, Department of Chemistry and Biochemistry, McCormick Rd., PO Box 400319,

Transcript of CHIRPED-PULSE FOURIER-TRANSFORM MICROWAVE SPECTROSCOPY OF THE PROTOTYPICAL C-H…π INTERACTION: THE...

CHIRPED-PULSE FOURIER-TRANSFORM MICROWAVE SPECTROSCOPY OF THE

PROTOTYPICAL C-H…π INTERACTION: THE BENZENE…ACETYLENE WEAKLY BOUND DIMER

Nathan W. Ulrich,a Nathan A. Seifert,b Rachel E. Dorris,a Ashley M. Anderton,a Rebecca A. Peebles,a

Brooks H. Pate,b Sean A. Peeblesa

a Department of Chemistry, Eastern Illinois University, 600 Lincoln Ave., Charleston, IL 61920

b University of Virginia, Department of Chemistry and Biochemistry, McCormick Rd., PO Box 400319, Charlottesville, VA 22904

Introduction• CH…p (aromatic) interactions– First suggested by Tamres (1952) 1

• HCCH pKa ~ 25– CH4 ~ 48, HCF3 ~ 25.5, HF ~ 3.17

• Few experimental results– Resonance enhanced

multiphoton ionization 2

– Co-crystal 3

2

1 M. Tamres, J. Am. Chem. Soc. 74 (1952) 3375. 2 E. Carrasquillo M., T. S. Zwier, D. H. Levy, J. Chem. Phys. 83 (1985) 4990.3 R. Boese, T. Clark, A. Gavezzotti, Helv. Chim. Acta, 86 (2003) 1085.

2.447 Å at 123 K 2.462 Å at 201 K

CC

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Previous Work

FBZ…HCl:M.E. Sanz,et al., J. Chem. Phys. 118 (2003) 9278. (BZ)2: M. Schnell, et al., Angew. Chem. Int. Ed., 52 (2013) 1. FBZ…HCCH: N. W. Ulrich, et al., Phys. Chem. Chem. Phys. 15 (2013) 18148. BZ…CF3H: J. C. López, et al., Angew. Chem. Int. Ed. Eng. 45 (2006) 290.

FC6H5…HCl

(C6H6)2

FC6H5…HCCH

C6H6…HCF3

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Ab Initio Calculations• MP2/6-311++G(2d,2p)• Fluorobenzene-HCCH– ~0.3 D induced dipole observed– Ab initio dipole components in

good agreement with experiment• Benzene-HCCH– C6v, ~0.5 D dipole

Gaussian 09, Revision C.01, M. J. Frisch, et al., Gaussian, Inc., Wallingford CT, 2010.

2.37 Å

2.38 Å

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Experimental• 0.1% benzene, 0.2% HCCH in Ne, ~1.7 atm– 5 nozzles @ 3.3 Hz, 8 FIDs/gas pulse, 2 ms chirp– Average of 520,000 FIDs– 13C12C5H6 in natural abundance

• Second broadband scan using C6H5D– 400,000 total FIDs, ~3.0 atm

• H13C12CH and H12C13CH on cavity FTMW– 0.5% benzene, 0.5% H13C12CH in He/Ne, ~2.8 atm– 1 nozzle @ 10 Hz, 1 FID/gas pulse

UVa CP-FTMW, Spring 2013

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Spectroscopic Parameters

Ab Initio C6H6 HCCH⋯C6H6 H⋯ 13C12CH

(near BZ)

C6H6 H⋯ 12C13CH

(away from BZ)13C12C5H6 HCCH⋯ C6H5D HCCH⋯

A / MHz 2846 – – – 2837(13) 2764.1(7)

B / MHz 1199 1148.89656(25) 1132.7251(4) 1114.2052(3) 1146.1883(4) 1146.2664(3)

C / MHz 1199 – – – 1141.1364(4) 1130.4918(3)

DJ / kHz – 1.207(3) 1.200(7) 1.151(6) 1.194(5) 1.179(3)

DJK / kHz – 19.977(11) 19.36(4) 19.36(3) 19.81(4) 19.347(12)

RMS / kHz – 2.2 1.8 1.4 3.7 6.0

N – 22 13 15 21 25

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r0 (Rcm) r0 (Rcm, θ) r0 (Rcm, ϕ) r0 (Rcm, θ, ϕ) rs Ab Initio

Rcm / Å 4.1546(1) 4.1560(8) 4.1547(1) 4.1554(5) 4.1320(15) 4.0387

θ / ° – 7.4(2.2) – 5.6(1.9) –

ϕ / ° – – 1.0(4) 0.8(2) –

RCH π⋯ / Å 2.4921(1) 2.5073(14) 2.4922(1) 2.5008(89) 2.4717(7) 2.3694

s / u Å2 0.038 0.025 0.017 0.015 –

Structure

RCC = 1.4043(12) Å

RCH = 1.0853(12) Å

RCC Lit.2 = 1.3969 Å

RCH Lit.2 = 1.0815 Å

q

f

r0: 2.4921(1) Års: 2.4717(7) Åre: 2.3694 Å

Rcm

RH…p

r0 (Rcm) r0 (Rcm, θ) r0 (Rcm, ϕ) r0 (Rcm, θ, ϕ) rs Ab Initio

Rcm / Å 4.1546(1) 4.1560(8) 4.1547(1) 4.1554(5) 4.1320(15) 4.0387

θ / ° – 7.4(2.2) – 5.6(1.9) –

ϕ / ° – – 1.0(4) 0.8(2) –

RCH π⋯ / Å 2.4921(1) 2.5073(14) 2.4922(1) 2.5008(89) 2.4717(7) 2.3694

s / u Å2 0.038 0.025 0.017 0.015 –

RCC = 1.1986(7) Å

Lit.1 = 1.203 Å

1 M. D. Harmony, et al., J. Phys. Chem. Ref. Data 8 (1979) 619.2 J. Pliva, et al., J. Mol. Spectrosc., 140 (1990) 214.

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Dipole Moments/Induction

m = 0.438(11) D

+

-ma,proj= +0.36 Dma,expt = ±0.0335(9) D

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Comparison…Complex ks / N m–1 EB / kJ mol–1 H…p distance / Å

BZ…HF 7.3 6.0 2.25(2)

BZ…HCl 8.0 8.6 2.35(2)

BZ…HBr 7.65 9.1 2.36(2)

BZ…HCF3 6.8 8.4 2.366(2)

BZ…HCN 6.6 8.9 2.38(2)

FBZ…HCl 3.9 4.4 2.456(16)

FBZ…HCCH 2.8 4.1 2.492(47)

BZ…HCCH 4.9(5) 7.1(7) 2.4921(1)

BZ…BZ 0.09 0.19 2.48(2)

BZ…HCCH co-crystal: 2.447 Å at 127 K

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BZ-HCN BZ-HF BZ-HCl BZ-HBr BZ-HCCH FBZ-HCl FBZ-HCCH0

5

10

15

20

25Binding Energies for XH…p Dimers of

Benzene and Fluorobenzene

CCSD(T)/CBS+BSSE

Pseudodiatomic

Binding Energy Calculations

ωB97XD/aug-cc-pvdz

M062X/aug-cc-pvdz

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Excited States• Three sets of transitions• Each has a different pattern• All lower than parent• Scale and have similar rotational constant to

parent• Could be intermolecular vibrational modes

J = 4 3

12Frequencies: M. Böning, et al., ChemPhysChem 14 (2013) 837.

x1

n 132 cm-1

x2

n 94 cm-1

x2

n 62 cm-1

Intermolecular Vibrational Modes?J = 5 4

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Summary, Conclusions, What’s Next? • Trimer(s)? – still unassigned lines with some

interesting patterns…• Need to understand excited states• A reliable frequency calculation would be nice

Trimers: A. Fujii, et al., J. Phys. Chem. A 108 (2004) 2652.

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Acknowledgements• RUI grant CHE-1214070 (EIU) and MRI-R2

grant CHE-0960074 (UVa) • Pate lab– Brooks Pate– Nate Seifert

• EIU Students – Anu Akmeemana– Cori Christenholz– Lena Elmuti

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Complex

BZ…HF

BZ…HCl

BZ…HBr

BZ…HCF3

BZ…HCN

FBZ…HCl

FBZ…HCCH

BZ…HCCH

BZ…BZ

[BZ…HF] F.A. Baiocchi, et al, J. Phys. Chem., 87, (1983) 2079.

[BZ…HCl] W.G. Read, et al, J. Chem. Phys., 78, (1983) 3501.

[BZ…HBr] S.A. Cooke, et al, Chem. Phys. Lett., 272, (1997) 61.

[BZ…HCF3] J.C. Lopez, et al, Angew. Chem., Int. Ed., 45, (2006) 290.

[BZ…HCN] H. S. Gutowsky, et al, J. Chem. Phys., 103, (1995) 3917.

[FBZ…HCl] M.E. Sanz, et al, J. Chem. Phys., 118, (2003) 9278.

[FBZ…HCCH] N. W. Ulrich, et al, Phys. Chem. Chem. Phys., 15, (2013) 18148.

[BZ…HCCH] N. W. Ulrich, et al, Phys. Chem. Chem. Phys., 16, (2014) 8886.

[BZ…BZ] E. Arunan, et al, J. Chem. Phys., 98, (199), 4294; M. Schnell, et al,

Angew. Chem. Int. Ed., 52, (2013), 5180.

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DFT Calculation for XH…p Interactions• Usual method is MP2/6-311++G(2d,2p)– Need a faster but equally accurate computational

approach

• G09 incorporates new DFT functionals designed for dispersion

2.38 Å

?

?2.37 Å

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MP2 wB97XDM062X

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JK' ← JK" |M| Number of

electric fields

30 ← 201 6

2 3

31 ← 210 6

40 ← 303 4

RMS: 5.8 kHz

μ: 0.438(11) D

Estimates of the H π distance range from 2.20 to 2.61 Å,35, 36 with high level ⋯CCSD(T)/aug-cc-pVTZ calculations predicting a distance of ~2.50 Å

M06-2X/6-311+G(d,p) calculation giving an H π distance of 2.393 Å and a binding ⋯energy of 12.2 kJ mol–1.39