Investigation of the Use of He-Diatomic Van der Waals Complexes as a Probe of Time Reversal Violation Jacob Stinnett, Dr. Neil Shafer-Ray, and Dr. Eric Abraham Homer L. Dodge Department of Physics University of Oklahoma This work was funded by the National Science Foundation (NSF ) 66 th OSU International Symposium on Molecular Spectroscopy June 24, 2011

Outline Motivation A remarkable observation of pure Stark spectroscopy in NO Simple vector model of a extremely weak He-NO van der Waals complex Suspicions Implications for an e-EDM measurement

Fabry-Pérot Type Resonator: Spherical Reflectors PbF Fourier Transform Microwave Spectrometer: Pure rotational absorption spectrom of the X 1 state of PbF. (Collaborators Jens-Uwe Grabow, Richard Mawhorter Hanover Germany)

Many e-EDM candidates require a large (~10kV/cm) field to become sensitive. Similar curves for BaF, HgF, YbF

This study was motivated a series of remarkable experiments involving pure Stark spectroscopy of the NO molecule.

Chem Phys Let A DC electric field of order 14 v/cm is crossed with an RF electric field of similar amplitude. At resonant frequencies, the population of NO, as viewed at non-state selective detector, is observed. Non state-selective 266nm ionization

Caceres et al measured a completely linear Stark effect in NO with simple transitions given by for J U =1/2, 3/2, and 5/2 D = (2) Debye Ap J 161 (1970) 779 BUT... D= (4) Debye CPL 426 (2006)214 Chem Phys Let

Two 2  1/2 electronic states form the ground state Z Y X  - [R xz -, R yz +]  + [R xz +, R yz -] Y Z X  = |  +  |= 1/2 gives projection of angular momentum on the nuclear axis: orbital a.m. (=1 for  states) spin a.m. ( ±1/2 because this is a 2  state.)

Motion of the Nuclei Although the electrons are light, their net angular momentum is not much smaller than that of the nuclei. Nuclei move as a symmetric top.

Combine to form  + wave function Combine to form  - wave function PARITY In the absence of an applied field, the wave functions are eigenvectors of parity and hence have no net dipole moment. Combined electronic and nuclear motion, DE<<  U 

up down For a strong electric field, the wave functions are either pointed up or down and one expects a linear Stark effect. Combined electronic and nuclear motion DE>>  U 

Motivation The Stark effect in NO is described by D is the dipole moment of NO E is the electric field Parity splitting ~= 10 GHz for 2 Π 1/2 NO ~= 10 MHz for 2 Π 3/2 NO

Motivation What suppressed the parity +MAGIC

“At present we have no explanation why the best fit is obtained with the resonant transition calculated with eq 2.” In this work we investigate the possibility that a novel He-NO van der Waals complex is responsible for this behavior.

N Possible He-NO Rydberg-Like van der Waals Complex O He (1) He must be far enough away so that D He <<D NO. (2) He must be close enough so that the He-NO van der Waals interaction is stronger than the parity splitting. Possible for He-NO( 2  3/2 ) at ~ 20 Angstroms.

Because the van der Waals energy must be much less than the rotational energy, the interaction may be treated as a perturbation to the NO spin rotational Hamiltonian

For the case of dipole-flipping transitions with |M He |=J He = |M| = ½,  =3/2, this reduces to This theory leads to a linear Stark effect that follows a simple vector model at low fields. (Ignoring E D induced )

A Simple Vector Model This simple model allows us to recover their formula. 3

Our model explains lines that Caceras et al have assigned to a J=3/2, J=5/2 transition. It also does a reasonable job predicted the substructure surrounding these lines. For the J U = 1/2 line, this vector model can not explain the observation. Experimental Theoretical

The He-NO bond distance required to suppress the parity splitting leads to a polarized He atom that changes the magnitude of the Stark interaction by much more than 0.2%.

Suspicions Chem Phys Let

1)A simple model indicates that the polarizability of a He-NO complex may be much greater than that of NO and gives reasonable agreement to the J=3/2 and J=5/2 lines observed by Caceres et al. 2)We cannot explain the magnitude of the linear Stark effect observed by Caceres et al and suspect their data analysis may be flawed. It is likely that their data is probing a known rather than exotic He-NO species. 3)He-[eEDM molecule] clusters formed in laser ablation sources may have increased polarizability and hence be worth investigating. Conclusions

Acknowledgements Dr. Neil Shafer Ray Dr. Eric Abraham NSF

Questions?

NO( 2  3/2 )-He(slow moving) + h RF  NO( 2  3/2 )-He(fast moving) NO( 2  3/2 )-He(fast moving) + NO  NO( 2  1/2 ) + He + NO + kinetic energy Resonant thermalization of the Omega-Doublet energy (120 cm -1 /molecule) and transverse kinetic energy of the beam (~1E-3 cm -1 / molecule).

Zeeman-effect in PbF(X 1 ) pure rotational spectra B = 0  M = 0  M = +/-1 ~3 kHz FREQUENCY / MHz