ROTATIONAL SPECTROSCOPY OF CO SOLVATED ROTATIONAL SPECTROSCOPY OF CO SOLVATED WITH WITH PARAPARA-H-H22 MOLECULES MOLECULES

Paul Raston and Wolfgang JägerDepartment of Chemistry, University of Alberta, Edmonton, AB Canada

OSU 2009

S. Baroni and S. Moroni, ChemPhysChem 6, 1884 (2005)

parapara-H-H22 clusters clusters

*P. Sindzingre, D. M. Ceperley, M. L. Klein, Phys. Rev. Lett. 67, 1871 (1991)

Low temperature (<2 K) para-H2 clusters are liquid like

Small pH2 clusters predicted to be superfluid below ~2 K.*

Rotational temperature of seeded clusters <1 K

In this study NpH2<8

Sample & conditionsSample & conditions

Typically used 0.05-1% CO + 1-10% pH2 in Helium up to 150 bar

Nozzle cooled down to -40°C

Normal H2 (75% ortho- + 25% para-) converted to >97% pH2 in catalytic converter held at <20K for several hours

I. F. Silvera, Rev. Mod. Phys. 52, 393 (1980)

FTMWFTMW spectrometerspectrometer

Pulsed molecular beam polarized with MW’s: Coherent emission is recorded

Good up to ~27 GHz, below which 6 (pH2)N-CO end-over-end transitions should lie

paraparaHH22-CO dimer-CO dimer

A.V. Potapov, L.A. Surin, V.A. Panfilov, B.S. Dumesh, T.F. Giesen, S. Schlemmer, P.L. Raston and W. Jäger, in preparation.

We know 101-000 transition frequency for N=1 to within ±50 kHz

0

5

10

15

20

25

C O H para 2

J j l, , C O

00 010 1

20 2

30 3

50 5

60 6

40 4

11 0211

31 2

41 3

51 4

61 5

111

21 2

31 3

41 4

51 5

011

11 2

21 3

31 4

41 5

6 61

K e=0( )

K e=1( )

K= (f)1

K e=0( ), =1b ,C O

c

a

b

O

C

H 2

N0 1 2 3 4 5 6 7 8 9

Fre

quen

cy /

MH

z

0

10000

20000

30000

40000

50000

TheoryIRMW

ppHH22-CO-CO

Previous IR studyPrevious IR study

S. Moroni, M. Botti, S. De Palo, A. R. W. McKellar, J. Chem. Phys. 122, 094314 (2005)

R1(0) line observed for NpH2<18

Not able to fully separate rotational and vibrational contributions to line position

N

0 1 2 3 4 5 6 7 8 9

Wav

enum

ber

/ cm

-1

2142.4

2142.6

2142.8

2143.0

2143.2

2143.4

2143.6

2143.8

2144.0

2144.2

2144.4

N0 1 2 3 4 5 6 7 8 9

Fre

quen

cy /

MH

z

0

10000

20000

30000

40000

50000

TheoryIRMW

MW predictions from:MW predictions from:

Assumption that the vibrational shift scales linearly with N

S. Moroni, M. Botti, S. De Palo, A. R. W. McKellar, J. Chem. Phys. 122, 094314 (2005)

MW predictions from:MW predictions from:

Assumption that the vibrational shift scales linearly with N

Reptation Monte Carlo simulations

S. Moroni, M. Botti, S. De Palo, A. R. W. McKellar, J. Chem. Phys. 122, 094314 (2005)

N0 1 2 3 4 5 6 7 8 9

Fre

quen

cy /

MH

z

0

10000

20000

30000

40000

50000

TheoryIRMWCol 1 vs Col 6

N0 1 2 3 4 5 6 7 8 9

Fre

quen

cy /

MH

z

0

10000

20000

30000

40000

50000

TheoryIRMWCol 1 vs Col 6

MW linesMW lines

N=2 found close to IR predicted value

N0 1 2 3 4 5 6 7 8 9

Fre

quen

cy /

MH

z

0

10000

20000

30000

40000

50000

TheoryIRMW

MW linesMW lines

N=3-6 increasingly further from IR predicted values

N0 1 2 3 4 5 6 7 8 9

Fre

quen

cy /

MH

z

0

10000

20000

30000

40000

50000

TheoryIRMWCol 1 vs Col 6

MW linesMW lines

Turnaround of rotational frequency in going from N=6 to 7

N

Wav

enum

ber

/ cm

-1

2141.8

2142.0

2142.2

2142.4

2142.6

2142.8

2143.0

2143.2

2143.4

ActualAssumed (linear shift with N)

N

0 1 2 3 4 5 6 7 8

Fre

quen

cy /

MH

z

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Difference

Vibrational shiftVibrational shift

N

Wav

enum

ber

/ cm

-1

2141.8

2142.0

2142.2

2142.4

2142.6

2142.8

2143.0

2143.2

2143.4

ActualAssumed (linear shift with N)

N

0 1 2 3 4 5 6 7 8

Fre

quen

cy /

MH

z

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Difference

Vibrational shiftVibrational shift

Switched IR assignment for N=6 & 7

N0 1 2 3 4 5 6 7 8 9

Fre

quen

cy /

MH

z

12000

14000

16000

18000

20000

22000

24000

12161316

((ppHH22))NN--1313CC1616O MW linesO MW lines

((ppHH22))NN--1313CO MW linesCO MW lines

N0 1 2 3 4 5 6 7 8 9

Fre

quen

cy /

MH

z

12000

14000

16000

18000

20000

22000

24000

12161316

((ppHH22))NN--1313CO MW linesCO MW lines

Number of pH2 molecules

1 2 3 4 5 6 7 8

1216

/131

6

1.00

1.01

1.02

1.03

1.04

1.05"free" CO

solid pH2

SummarySummary

1216 1316 Assignment

22200.54 22054.30 (pH2)2-CO

16455.81 16326.93 (pH2)3-CO

15107.44 14959.44 (pH2)4-CO

14633.25 14473.32 (pH2)5-CO

13243.82 13096.04 (pH2)6-CO

17723.12 17403.17 (pH2)7-CO

 

15834.58 15727.36 pH2-He-CO

*Tentative

OutlookOutlook

MW transitions of (pH2)N=2-7-CO (1216 and 1316) measured and assigned

Turnaround in rotational frequency observed in going from N=6 to 7

Extend frequency range of spectrometer and search for N=8 at 30-40+ GHz….

Find 1218 and 1318 lines

AcknowledgementsAcknowledgements

Jäger group

Xu group

A.R.W. McKellar

Funding: University of Alberta Natural Science and Engineering Research Council of Canada Canada Foundation for Innovation Alberta Science and Research Investments Program

PESPES

• Reptation Monte Carlo algorithm used to simulate rotational dynamics for NpH2<18

• N=incremental density distribution

C O

AssignmentAssignment

Ratio of line intensities for 2 different gas mixtures differing only in the [pH2]; The 2nd mixture contained 0.125x the [pH2] in the 1st

N

1 2 3 4 5 6 7 8

Inte

nsit

y ra

tio

e0

e1

e2

e3

e4

e5

e6

e7

Assignments mostly from concentration dependence of line intensities

Comparison with HD solvated HCNComparison with HD solvated HCN

D. T. Moore, R. E. Miller, J. Chem. Phys. 119, 4713 (2003)

/ MHz

17722.8 17723.0 17723.2 17723.4 17723.6