The rotational spectra of helium-The rotational spectra of helium-pyridine and hydrogen molecule-pyridine and hydrogen molecule-

pyridine clusterspyridine clusters

Chakree Tanjaroon and Wolfgang Jäger

Pyridine moleculePyridine molecule

The C5H5N structure is similar to C6H6.

Large aromatic surfaces = many Van der Waals binding sites.

A strong polarizer.

N-C3 = 2.805 Å

Surface area 6.2 Å2

Dipole moment = 2.2 debye

M. J. Heather, D. W. H. Swenson, and C. E. Dykstra. J. Phys. Chem. A, 110, 6399-6407 (2006).

Predicted (HPredicted (H22))2020-C-C66HH6 6 clusterclusterH2 7 above--6 along the edge--7 below!

The axial H2 are slippery (floppy).

The dimersThe dimers Helium-pyridine Hydrogen molecule-

pyridine

MP2 calculations show the T-shaped configuration is most stable.

B = 59.3 cm-1

I = 1 (oH2)

I = 0 (pH2)

(De = 90 cm-1) (De = 327 cm-1)

Rotation of HRotation of H2 2 over Cover C55HH55N surfaceN surface“H-bond” breaking motion

(-327 cm-1) (-290 cm-1)40 cm-1 up hill

More repulsive

FTMW FTMW ExperimentExperiment

For details see: V. N. Markov, Y. Xu, and W. Jager, Rev. Sci. Instrum. 69, 1198, 4061 (1998).

He-C5H5N: 0.05% pyridine at 8.0 - 40.0 atm. helium

H2-C5H5N: 0.05% pyridine + 5.0 % H2 at 40.0 atm helium

Experimental ResultsExperimental ResultsHeHeNN-C-C55HH55NN

He1-C5H5N He2-C5H5N12 R-branch transitions.

9 a-type and 3 c-type.

39 hyperfine components.

5 R-branch transitions.

All a-type.

18 hyperfine components.

The 0The 000001101 01 transitiontransition

He1-C5H5N He2-C5H5N

The narrow splitting = He atom tunnelling?

1 of 3 hyperfine components 1 of 3 hyperfine components

Parameter He1-C5H5NThis

experiment

He1-C5H5N**Fit to

experimental ABC

He1-C5H5NMP2/augcc-

pvdz

He1-C6H6 LIF

Experiment

A(MHz) 3875.2093(48) 3869.115 4062.5833 -

B(MHz) 3753.2514(45) 3771.568 3933.7093 3670(640)

C(MHz) 2978.4366(81) 2959.210 2906.1860 2950(190)

R(Å) - 3.506 3.23 3.17(37)

(°) 7.3 0.061 3.7 0.0

(fit) 3.9 kHz - - -

HeHe11-C-C55HH55N:N: The rotational constants and some structural parameters.

S. M. Beck, M. G. Liverman, D. L. Monts, and R. E. Smalley, J. Chem. Phys., 70(1), 232-237 (1979).

** Z. Kisiel, P. W. Fowler, and A. C. Legon, J. Chem. Phys. 95(4), 2283-2291, (1991).

Parameter He2-C5H5NThis experiment*

He2-C5H5NFit

(TopToP)A(MHz) 3177.27(50) 3070.5431

B(MHz) 2707.184(50) 2824.7893

C(MHz) 2980.374(67) 2791.7481

R(Å) (X-He2)Rcom = 3.48

He1-He2 = 1.30

HeHe22-C-C55HH55N:N: The rotational constants and some structural parameters.

Parameter (MHz)

He1-C5H5N He2-C5H5N Ar-C5H5N

DJ 0.12408(55) 0.2259(53) 0.00358(5)

DJK 0.1200(43) -0.397(14) 0.0196(1)

DK -0.2451(25) - -0.023(15)

d1 0.00427(27) - -

d2 -0.00016(10) - -

HJ 0.003053(35) - -

HJK -0.006588(473) - -

HK 0.004114(587) - -

1.5(cc) 5.0122(64) 5.104(40) -

0.25(bb-aa) 1.5589(19) 1.5735(97) -

The distortion constants for He1-C5H5N and He2-C5H5N.

T.D. Klots, T. Emilsson, R. S. Ruoff, and H. S. Gutowsky. J. Phys. Chem. 93, 1266 (1989)

Experimental ResultsExperimental Results(H(H22)-C)-C55HH55NN

o(H2)-C5H5N p(H2)-C5H5N

(V0) (V1)

[ jH2= 1 ] [ jH2= 0 ]

Ground state Excited state

The 0The 000001101 01 transition, (Vtransition, (V00))

o(H2)-C5H5N: 11 a-type transitions, 52 hyperfine components fitted.

o(H2)-C5H5N p(H2)-C5H5N

100 shots, S/N = 2000 200 shots, S/N =200

p(H2)-C5H5N: 4 a-type transitions fitted.

Hyperfine structures: o(HHyperfine structures: o(H22))CC55HH55NN

Fig. above illustrates the hyperfine splittings for 000 101 transition. The larger quadrupole splittings 1.5-2.0 MHz. The smaller spin-rotation splittings are 0.05 MHz.

(MHz)

F =1F=1

F =1F=2

F =1F=0

000 101

J = 1J = 1 J J = 2, = 2, K = 0 |KK = 0 |Kaa| = 1| = 1

111212

101202

110211

The observed 111212 and 110211 lines are displaced 1514 MHz from the band center due entirely to the asymmetry splitting. Highest transition is J=3J=4.

The rotational and distortion constants for o(H2)-C5H5N and p(H2)-C5H5N.

Parameter (MHz)

o(H2)-C5H5NThis

experiment

p(H2)-C5H5NThis experiment*

(H2)-C5H5NMP2/augcc-pvdz

(T-shaped)

A 4673.016(11) 4945.8035(22) 4812.9623

B 4476.9953(22) 4627.9071(8) 4639.6078

C 2962.6876(33) 2964.4795(8) 2908.0300

DJ 0.03596(94) 0.04292(9) -

DJK -0.0858(32) - -

DK 0.0602(24) - -

d1 0.01724(53) - -

d2 -0.00458(13) - -

C5H5N: A = 6039.2516(6), B = 5804.9116(6), C = 2959.2117(6) MHz.

The quadrupole and spin-rotation coupling constants, and the bond distance R for oH2-C5H5N.

Parameter (MHz)

o(H2)-C5H5NThis

experiment

C5H5N Free

H2

eQqaa -4.884(7) -4.908(3) -

eQqbb 1.451(7) 1.434(3) -

eQqcc 3.433(10) 3.474(3) -

Maa 0.0124(45) - -

Mbb 0.0208(22) - 0.1139 (M)

Mcc 0.0205(12) - -

R(parallel) 3.76(3) Å - -

R(perpendicular) 3.58(3) Å - -

G. O. Sørensen. J. Molecular Spectroscopy, 22, 325(1967). N. F. Ramsey. Phys. Rev. 85, 60 (1952).

ConclusionConclusion• He1-C5H5N T-shaped complex.

• (H)2-C5H5N T-shaped complex.

• (He)2-C5H5N nearly T-shaped. Helium atoms lie on the same ring side.

AcknowledgementsAcknowledgements• Natural Sciences and Engineering Research Council of

Canada and Alberta Ingenuity Fund for the financial supports.

• Qing Wen and Jen Landry for help with the FTMW spectrometer.

• Thank you for your attention!

More He/H2 clusters MW talks by our group:

TE02: Jen N. Landry TE03: Julie M. Michaud RI01: Wolfgang Jäger