Probing the Dependence of the H2/D2 + ICl/I2 Entrance Channel Interactions on

Intermolecular Orientation

Joshua P. Darr, Andrew C. Crowther, and Richard A. Loomis*

Washington University in St. Louis

Department of Chemistry

June 22, 2005

The Ohio State University: 60th International Symposium on Molecular Spectroscopy

Introduction

• Moving from 3-atom Rg···XY systems to 4-atom H2···XY complexes

• Look for multiple ground state conformers that can access different regions of an excited state potential energy surface

• Investigate the importance of electrostatic effects on long-range interactions

3.0 3.5 4.02.5

0

1000

2000

17500

Tra

nsi

tion

En

ergy

(cm

–1)

I–Cl Distance (Å)

X 1+

B 30+

Z 1 B 0+

18000

V.P.

Fluorescence

Exc

itat

ion

LIF of H2···ICl in the ICl B–X Region

×100

17700 17750 17800 17850

ICl B

–X F

luor

. (ar

b. u

nit

s)

Wavenumbers (cm–1

)

LIF of H2···ICl Complexes (ICl B–X, 2–0 and 3–0 Region)

**

*

* *

*

*I2

*I35ClB–X, 2–0 I35Cl

B–X, 3–0

Action Spectroscopy of H2···ICl B–X, 2–0

I 2P3/2 + Cl 2P1/2

I+ 3P2 + Cl– 1S2

I 2P3/2 + Cl 2P3/2

3.0 3.5 4.02.5

0

1000

2000

17500

41000

Tra

nsi

tion

En

ergy

(cm

–1)

I–Cl Distance (Å)

X 1+

B 30+

Z 1

B 0+

E 0+

18000

39000P

um

p

ICl EXFluorescence

Pro

be

Vib.Pred.

×100

17700 17750 17800 17850

I35C

l E–X

Flu

or.

Wavenumbers (cm–1

)

ICl B

–X F

luor

.Action Spectroscopy of H2···ICl Complexes (ICl B–X, 2–0 Region)

Action SpectrumProbe: I35Cl E–B, 10–1

LIF Spectrum

H2···I35ClH2···I35Cl

H2···I35Cl

*

*

*

**

* ****

*

H2···I35Cl

17850 17900 17950 18000

5% H2 in He carrier gas

I35C

l E–X

Flu

or. (

arb

. un

its)

Wavenumbers (cm–1

)

Action Spectroscopy of H2···ICl Complexes (ICl B–X, 3–0 Region)

Probe: I35Cl E–B, 11–2

* **

10% H2 in He carrier gas

Assigning o,p-H2···ICl Features (ICl B–X, 3–0 Region)

~5% n-H2 in He

~5% p-H2 in He

* **

**

*

17850 17900 17950 18000I35C

l E–X

Flu

or.

Wavenumbers (cm–1

)

I35C

l E–X

Flu

or.

o-H2···I35Cl

o-H2···I35Cl

o-H2···I35Cl

p-H2···I35Cl

p-H2···I35Cl p-H2···I35Cl

Rotational Contour of Lower Energy H2···I35Cl Feature

-2 -1 0

T-shaped He···I35

Cl B–X, 3–0

I35C

l E

X F

luor

. (ar

b. u

nit

s)

Relative Energy (cm–1

)

Asymmetric o-H2···I35Cl B–X, 3–0

Assigning the Lower Energy Features (ICl B–X, 3–0 Region)

17850 17900 17950 18000

5% H2 in He carrier gas

I35C

l E–X

Flu

or. (

arb

. un

its)

Wavenumbers (cm–1

)

Asymmetric o-H2···I35Cl

Asymmetric p-H2···I35Cl

H2 and ICl(X,v=0) Electrostatic Potentials

-Gaussian 03

Possible H2···ICl(X,v=0) Structures

ortho-H2 (j=1)para-H2 (j=0)

C2v

Asymmetric

Assigning the H2···I35Cl Features (ICl B–X, 3–0 Region)

17850 17900 17950 18000

5% H2 in He carrier gas

I35C

l E–X

Flu

or. (

arb

. un

its)

Wavenumbers (cm–1

)

C2v p-H2···I35Cl

Asymmetric o-H2···I35Cl

Asymmetric p-H2···I35Cl

C2v o-H2···I35Cl

Determining the C2v, Prolate SymmetricTop H2···ICl(X,v=0) Binding Energy

I 2P3/2 + Cl 2P1/2

I+ 3P2 + Cl– 1S2

I 2P3/2 + Cl 2P3/2

3.0 3.5 4.02.5

0

1000

2000

17500

41000

Tra

nsi

tion

En

ergy

(cm

–1)

I–Cl Distance (Å)

X 1+

B 30+

Z 1

B 0+

E 0+

18000

39000P

um

p

ICl EXFluorescence

Pro

be

Determining the C2v, Prolate SymmetricTop H2···ICl(X,v=0) Binding Energy

C2v, Prolate Symmetric TopAsymmetric

H2–ICl Distance (Å)

En

ergy

(cm

–1)

H2 +ICl(X,v=0)

H2 +ICl(B,v=2)

Pump

Probe

×1000

17700 17750 17800 17850

I35C

l E–X

Flu

or. (

arb

un

its)

Wavenumbers (cm–1

)

Determining the C2v, Prolate SymmetricTop H2···ICl(X,v=0) Binding Energy

H2···I35Cl C2v, Prolate Symmetric Top Continuum

D0=186.4(3) cm–1

2.0 2.5 3.0 3.5 4.0 4.50

1000

17000

17200

17400

17600

En

ergy

(cm

-1)

I - Cl Distance (Å)

Determining the H2···ICl(A,v) Binding Energy of the Asymmetric Conformer

X 1+

Pu

mp

Pro

be

A 31

I 2P3/2 + Cl 2P3/2

-150

-100

-50

0

16700

16800

16900

En

ergy

(cm

–1)

H2 to ICl Distance

H2 + ICl(X,v=0)

H2 + ICl(A,v=21)

H2 + ICl(A,v=22)

H2 + ICl(A,v=20)v = –2 Vib. Prediss.

v = –1 Vib. Prediss.P

um

p

Pu

mp

Determining the H2···ICl(A,v) Binding Energy of the Asymmetric Conformer

Determining the H2···ICl(A,v) Binding Energy of the Asymmetric Conformer

16825 16830 16835 16840 16845I35C

l –A

Flu

or.

Wavenumbers (cm–1

)

17030 17035 17040 17045

I35C

l –A

Flu

or.

Wavenumbers (cm–1

)

v=24

v = –2

v = –1

16970 16975 16980 16985I35C

l –A

Flu

or.

Wavenumbers (cm–1

)

p-H2···ICl

v=23v=21

o-H2···ICl

16900 16905 16910 16915 16920I35C

l –A

Flu

or.

Wavenumbers (cm–1

)

o-H2···ICl

v=22

p-H2···ICl

p-H2···ICl

• The spectroscopic shifts of the complexes from the monomers can then be used to bracket the ground state binding energies– o-H2···I35Cl(X,v=0) 82.8(3) D089.6(3) cm–1

Determining the H2···ICl(X,v=0) Binding Energy of the Asymmetric Conformer

• The observed vibrational distributions place limits on the binding energy of the excited state complexes– o-H2···I35Cl(A,v=21) D082.9 cm–1

– o-H2···I35Cl(A,v=22) D074.9 cm–1

69.5(3)-76.3(3) 59.4(1.0)-67.3(3)

• o-H2···ICl(B,v=3) p-H2···ICl(B,v=3)

Summary of H2···I35Cl Binding Energies

AsymmetricC2v Sym. Top

• o-H2···ICl(X,v=0) p-H2···ICl(X,v=0)

186.4(3) 82.8(3)-89.6(3) 156.8(1.3) 70.0(1.0)-77.9(3)

Action Spectroscopy of H2···ICl Complexes (ICl B–X, 3–0 Region)

17850 17900 17950 18000

10% H2 in He carrier gas

I35C

l E–X

Flu

or. (

arb

. un

its)

Wavenumbers (cm–1

)

-200

-150

-100

-50

0

17750

17800

p-H2···I35

Clo-H2···I35

Cl

En

ergy

(cm

–1)

Energies of Ground and Excited StateH2···I35Cl Levels

C2v, ProlateSymmetric Top

AsymmetricDelocalized

H2 + I35Cl(X,v=0)

H2 + I35Cl(B,v=3)

17800 17850 17900 17950 18000 18050

C2v, Prolate Symmetric Top

Flu

ores

cen

ce I

nte

nsi

ty

Wavenumbers (cm–1)

Asymmetric

Spectroscopy of D2···ICl Complexes (ICl B–X, 3–0 Region)

D2···I35Cl

D2···I35Cl

17820 17830 17840 17850 17860

T-shaped

Flu

ores

cen

ce I

nte

nsi

ty

Wavenumbers (cm–1)

Asymmetric

Spectroscopy of D2···ICl Complexes (ICl B–X, 3–0 Region)

D2···I35Cl

He···I35Cl

I35Cl

17960 17980 18000 18020 18040

C2v, Prolate Symmetric Top

Flu

ores

cen

ce I

nte

nsi

ty

Wavenumbers (cm–1)

Spectroscopy of D2···ICl Complexes (ICl B–X, 3–0 Region)

D2···I35Cl

100 105 110 115 120 125 130

C2v, o-H2···I2 continuum

D0 = 118.8(1.9) cm–1

I 2 –

A, 0

–v† F

luor

. (ar

b. u

nit

s)

Energy Rel. to I2 B–X, 19–0 (cm–1

)

C2v, p-H2···I2 continuum

D0 = 102.7(9) cm–1

Determining the C2v, Prolate SymmetricTop H2···I2(X) Binding Energy

Binding Energies of Different Conformers of the Dihalogen Complexes

T-shaped/Asymmetric

Linear/C2v Sym. Top

• o-H2···I2

• p-H2···I2

118.9(1.9) 91.3-93.3 (Levy) 102.7(9) --

• He···ICl• Ne···ICl

22.0(2) cm–1 16.6(3) cm–1

84(1) 70(5)

• o-H2···ICl

• p-H2···ICl 186.4(3) 82.8(3)-89.6(3)156.8(1.3) 70(1)-77.9(3)

• p-D2···ICl

• o-D2···ICl223.9(2.4) 97.3(8)-103.9(3) 202(3) 87.7(3)-95.2(2)

Acknowledgements

• Prof. Loomis, Dave Boucher, John Glennon, Andrew Crowther, and other previous group members

• Prof. Anne McCoy, OSU

• Prof. Ben McCall, Univ. of Illinois

• Prof. Lev Gelb, Washington Univ.

0 50 100 150

I35C

l E–X

Flu

or.

Shift from I35

Cl B–X, 2–0 (cm–1

)

Assigning o,p-(H2)1···ICl Features

0 50 100 150

I35C

l E–X

Flu

or.

Shift from I35

Cl B–X, 3–0 (cm–1

)

Asymmetric H2···I35Cl

Asymmetric H2···I35Cl

C2v p-H2···I35Cl

C2v p-H2···I35Cl

C2v o-H2···I35Cl

C2v o-H2···I35Cl

• Bond lengths at this level of theory:– H2: 0.743 Å (0.741 Å exp.)

– ICl: 2.346 Å (2.319 Å exp.)

H2 and ICl(X,v=0) Electrostatic Potential Calculations

• Calculation performed on Gaussian 03 with CCSD optimized structures– H and Cl atom basis set: aug-cc-tzp

– I atom basis set: SDB-cc-tzp

Rotational Contour of Lower Energy C2v o-H2···I35Cl Feature

17802 17804 17806 17808 17810

I35C

l E–X

, 10–

v F

luor

.

Wavenumbers (cm–1

)

C2v o-H2···I35Cl

Action Spectroscopy of H2···ICl Complexes (ICl A–X, 21–0 Region)

100 120 140 160 180

C2v H2···I35

Cl

A–X, 19–0

C2v H2···I35

Cl

A–X, 19–0

I35

Cl A–X, 21–0

I37

Cl A–X, 21–0

I35C

l –A

, 4–v

Flu

or.

Shift from I35

Cl A–X, 19–0 (cm–1

)