Probing the Dependence of the H 2 /D 2 + ICl/I 2 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: 60 th International Symposium on Molecular Spectroscopy

Introduction Moving from 3-atom Rg···XY systems to 4-atom H 2 ···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

Transition Energy (cm –1 ) I–Cl Distance (Å) X 1+X 1+ B 3  0+ Z 1 B V.P. Fluorescence Excitation LIF of H 2 ···ICl in the ICl B–X Region

×100 LIF of H 2 ···ICl Complexes (ICl B–X, 2–0 and 3–0 Region) * * * * * * * I2I2 * I 35 Cl B–X, 2–0 I 35 Cl B–X, 3–0

Action Spectroscopy of H 2 ···ICl B–X, 2–0 I 2 P 3/2 + Cl 2 P 1/2 I + 3 P 2 + Cl – 1 S 2 I 2 P 3/2 + Cl 2 P 3/ Transition Energy (cm –1 ) I–Cl Distance (Å) X 1+X 1+ B 3  0+ Z 1 B 0 + E Pump ICl E  X Fluorescence Probe Vib. Pred.

×100 Action Spectroscopy of H 2 ···ICl Complexes (ICl B–X, 2–0 Region) Action Spectrum Probe: I 35 Cl E–B, 10–1 LIF Spectrum H 2 ···I 35 Cl * * * * * * * * * * *

Action Spectroscopy of H 2 ···ICl Complexes (ICl B–X, 3–0 Region) Probe: I 35 Cl E–B, 11–2 * **

Assigning o,p-H 2 ···ICl Features (ICl B–X, 3–0 Region) ~5% n-H 2 in He ~5% p-H 2 in He ** * * * * o-H 2 ···I 35 Cl p-H 2 ···I 35 Cl

Rotational Contour of Lower Energy H 2 ···I 35 Cl Feature Asymmetric o-H 2 ···I 35 Cl B–X, 3–0

Assigning the Lower Energy Features (ICl B–X, 3–0 Region) Asymmetric o-H 2 ···I 35 Cl Asymmetric p-H 2 ···I 35 Cl

H 2 and ICl(X,v  =0) Electrostatic Potentials -Gaussian 03

Possible H 2 ···ICl(X,v  =0) Structures ortho-H 2 (j  =1)para-H 2 (j  =0) C 2v Asymmetric

Assigning the H 2 ···I 35 Cl Features (ICl B–X, 3–0 Region) C 2v p-H 2 ···I 35 Cl Asymmetric o-H 2 ···I 35 Cl Asymmetric p-H 2 ···I 35 Cl C 2v o-H 2 ···I 35 Cl

Determining the C 2v, Prolate Symmetric Top H 2 ···ICl(X,v  =0) Binding Energy

C 2v, Prolate Symmetric Top Asymmetric H 2 –ICl Distance (Å) Energy (cm –1 ) H 2 + ICl(X,v  =0) H 2 + ICl(B,v=2) Pump Probe

×1000 Determining the C 2v, Prolate Symmetric Top H 2 ···ICl(X,v  =0) Binding Energy H 2 ···I 35 Cl C 2v, Prolate Symmetric Top Continuum D 0  =186.4(3) cm –1

Determining the H 2 ···ICl(A,v) Binding Energy of the Asymmetric Conformer X 1  + Pump Probe A 3  1 I 2 P 3/2 + Cl 2 P 3/2

H 2 + ICl(X,v  =0) H 2 + ICl(A,v=21) H 2 + ICl(A,v=22) H 2 + ICl(A,v=20)  v = –2 Vib. Prediss.  v = –1 Vib. Prediss. Pump Determining the H 2 ···ICl(A,v) Binding Energy of the Asymmetric Conformer

v=24  v = –2  v = –1 p-H 2 ···ICl v=23v=21 o-H 2 ···ICl o-H 2 ···ICl v=22 p-H 2 ···ICl

The spectroscopic shifts of the complexes from the monomers can then be used to bracket the ground state binding energies –o-H 2 ···I 35 Cl(X,v  =0) 82.8(3)  D 0  89.6(3) cm –1 Determining the H 2 ···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-H 2 ···I 35 Cl(A,v=21) D 0  82.9 cm –1 –o-H 2 ···I 35 Cl(A,v=22) D 0  74.9 cm –1

69.5(3)-76.3(3) 59.4(1.0)-67.3(3) o-H 2 ···ICl(B,v=3) p-H 2 ···ICl(B,v=3) Summary of H 2 ···I 35 Cl Binding Energies AsymmetricC 2v Sym. Top o-H 2 ···ICl(X,v  =0) p-H 2 ···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 H 2 ···ICl Complexes (ICl B–X, 3–0 Region)

Energies of Ground and Excited State H 2 ···I 35 Cl Levels C 2v, Prolate Symmetric Top Asymmetric Delocalized H 2 + I 35 Cl(X,v  =0) H 2 + I 35 Cl(B,v=3)

C 2v, Prolate Symmetric Top Fluorescence Intensity Wavenumbers (cm –1 ) Asymmetric Spectroscopy of D 2 ···ICl Complexes (ICl B–X, 3–0 Region) D 2 ···I 35 Cl

T-shaped Fluorescence Intensity Wavenumbers (cm –1 ) Asymmetric Spectroscopy of D 2 ···ICl Complexes (ICl B–X, 3–0 Region) D 2 ···I 35 Cl He···I 35 Cl I 35 Cl

C 2v, Prolate Symmetric Top Fluorescence Intensity Wavenumbers (cm –1 ) Spectroscopy of D 2 ···ICl Complexes (ICl B–X, 3–0 Region) D 2 ···I 35 Cl

Determining the C 2v, Prolate Symmetric Top H 2 ···I 2 (X) Binding Energy

Binding Energies of Different Conformers of the Dihalogen Complexes T-shaped/ Asymmetric Linear/ C 2v Sym. Top o-H 2 ···I 2 p-H 2 ···I (1.9) (Levy) 102.7(9) -- He···ICl Ne···ICl 22.0(2) cm –1 16.6(3) cm –1 84(1) 70(5) o-H 2 ···ICl p-H 2 ···ICl 186.4(3) 82.8(3)-89.6(3) 156.8(1.3) 70(1)-77.9(3) p-D 2 ···ICl o-D 2 ···ICl 223.9(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.

Assigning o,p-(H 2 ) 1 ···ICl Features Asymmetric H 2 ···I 35 Cl C 2v p-H 2 ···I 35 Cl C 2v o-H 2 ···I 35 Cl

Bond lengths at this level of theory: –H 2 : Å (0.741 Å exp.) –ICl: Å (2.319 Å exp.) H 2 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 C 2v o-H 2 ···I 35 Cl Feature C 2v o-H 2 ···I 35 Cl

Action Spectroscopy of H 2 ···ICl Complexes (ICl A–X, 21–0 Region)