Spectroscopic and Ab Initio Studies of the Open-Shell Xe-O 2 van der Waals Complex Qing Wen and Wolfgang Jäger Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada

2 Motivation to Study the Interactions of Xe with O 2 Laser-polarized 129 Xe (I = ½) significantly increases NMR signals In vivo 129 Xe imaging applications Paramagnetic O 2 (S =1) will cause rapid spin relaxation of 129 Xe 1 H & 129 Xe MRI of human lung [1] [1] Goodson, J. Magn. Reson. 155, 157 (2002); Mugler et al. Magn. Reson. Med. 37, 809 (1997).

3 Ab Initio Calculation Program: Molpro Package UCCSD(T) level of theory Basis sets: Xe: aug-cc-pVQZ-PP O: aug-cc-pVTZ Midbond functions (3s, 3p, 2d, 2f, 1g) Supermolecule approach Counterpoise correction O-O bond length fixed at Å [1] R  Xe OO [1] CRC Handbook of Chemistry and Physics 84th Ed. (CRC Press, Boca Raton, 2003).

4 Potential Energy Surface x / Å Global minimum at R= 3.9 Å;  = 90 , E = cm -1 y / Å Xe OO Energies in cm -1

5 Potential Energy Surface x / Å Local minimum at R = 4.4 Å;  = 0 , E = cm -1 y / Å Xe OO Energies in cm -1

6 Potential Energy Surface x / Å Transition state at R = 4.4 Å;  = 30 , E = cm -1 y / Å Energies in cm Xe OO

7 Fourier Transform Microwave Spectrometer Frequency range: 3-26 GHz 1% Xe, 1% O 2 in Ne at 5 atm

8 J = 2-1 Transition of 132 Xe-O 2 Interactions of the magnetic moment of the O 2 (S = 1) with Earth’s magnetic field

9 Helmholtz Coils

10 With the Use of Helmholtz Coils J = 2-1 transition of 132 Xe-O 2 J’-J”Frequency (MHz)

11 Proposed Coupling Scheme I  total symmetric  elec antisymmetric ( 3  - )  vib symmetric  spin symmetric (I tot = 0)  rot antisymmetric (K = 1,3,5…) O 2 : I 1 =I 2 =0 J K S  OO Xe used for O 2 -N 2 O [1] Rotational wavefunction: J, K, parity Spin wavefunction: S,  [1] Qian, Low, Seccombe, and Howard, JCP 107, 7651,7658 (1997).

12 Transition Frequencies of Ne-O 2 and Ar-O 2 J’-J” Ar-O 2 (MHz) 22 Ne-O 2 (MHz) 20 Ne-O 2 (MHz)

13 Proposed Coupling Scheme II j: rotational angular momentum of O 2 monomer. Quantum number j only can be odd number, 1, 3, 5,… J a : total angular momentum of O 2 monomer. K J j S JaJa K L Xe OO L: end-over-end rotational angular momentum of the complex. [1] van der Avoird, JCP 79, 1170 (1983). Proposed for Ar-O 2. [1]

14 Energy Level Diagram |K| = 0 even parity |K| = 2 even parity odd |K| = 1 even parity odd |K| = 0 odd parity J van der Avoird, JCP 79, 1170 (1983). Energy (MHz) 0 50 E = BJ(J+1)-D J J 2 (J+1) 2 no information about electron spin-spin and spin-rotation interactions.

15 Spectroscopic Constants and Structural Parameters 132 Xe-O 2 Ar-O 2 22 Ne-O 2 20 Ne-O 2 B (MHz) (2) (5) (7) (7) D J (kHz)46.428(8)361.98(5)2467.5(1)3053.7(1) R 0 (Å) R e (Å) (ab initio) 3.9

16 Hyperfine Structure of the J = 2-1 transition of 129 Xe-O 2 Interactions of the electron spin of O 2 (S =1) with the nuclear spin of 129 Xe (I = ½) I + J = F

17 Hyperfine Constants Magnetic hyperfine constants, b = b F -c/3, arising from 129 Xe (I = ½) and 131 Xe (I = 3/2) b F : Fermi-contact coupling constant c: Magnetic dipole-dipole coupling constant Nuclear Quadrupole coupling constant  aa arising from 131 Xe 129 Xe-O Xe-O 2 ratio ( 129 Xe/ 131 Xe) 131 Xe-N 2 b (MHz)0.42(2)-0.095(4)-4.4 g factor-3.4  aa (MHz) 0.624(2)0.290(2)

18 Summary Ab initio calculation shows that Xe-O 2 has a T- shaped equilibrium structure. Rotational spectra of Xe-O 2 were interpreted using a coupling scheme which first couples the electron spin to the rotational motion of O 2 monomer. Hyperfine structures due to non-zero nuclear spins of 129 Xe and 131 Xe were detected and analyzed.

19 Acknowledgements Jäger and Xu groups Graduate Students Association, University of Alberta