Anh T. Le and Timothy C. Steimle The electric dipole moment of Iridium monosilicide, IrSi Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ Lan Cheng and John F. Stanton The University of Texas at Austin, Austin, TX Michael D. Morse and Maria A. Garcia Department of Chemistry, University of Utah, Salt Lake City, UT 84112, USA The 68 th International Symposium on Molecular Spectroscopy, June 2013 Funded by DoE-BES

Motivation  Iridium containing molecules IrSi?

Previous work * Prof Morse’s group: Recorded 31 electronic bands  Recorded high resolution LIF of the (6,0)[16.0]1.5 - X 2  5/2 bands for 191&193 IrSi (lowest angular momentum quantum number)  Analyzed, determined the fine and hyperfine parameters  Recorded & Analyzed Stark spectra to determine the molecular dipole moments for the X 2  5/2 and [16.0]1.5(v=6) states

Experiment method Ablation laser CW dye laser SkimmerStark Plates Well collimated molecular beam Rot.Temp.<20 K Electric field ~ 4000 V/cm Resolution ~30 MHz Gated photon counter

(6,0)[16.0]1.5-X 2  5/2 band Large isotopic shifts (1.5cm -1 ) between 191 IrSi, 193 IrSi Formed a head quickly due to large difference in rotational constants Highly overlapped Complicated spectrum Observation Need to understand the field free spectrum to be able to study the Stark spectra

(6,0)[16.0]1.5-X 2  5/2 band Observation (cont.) Resolution ~30 MHz

1.Effective Hamiltonian H eff = H so + H rot + H mhf (Ir)+ H eQq (Ir) Modeling the (6,0)[16.0]1.5-X 2  5/2 band system Ir(I=3/2) Parameters: B, h 5/2 ( 191,193 Ir) and eQq 0 ( 191,193 Ir) for the X 2  5/2 (v=0) state,T 00, B, h 3/2 ( 191,193 Ir) and eQq 0 ( 191,193 Ir) for the (6,0)[16.0] x16 Matrix representation: Hund’s case (a bJ ) coupled basis set:  Eigenvalues & Eigenvectors

Ready for Stark measurement & analysis Stark effect (next slide) Predicted spectra

2339 V/cm|| 0V/cm P(5/2) under applied electric field 1754 V/cm|| LIF signal 191P(11/2) 1169 V/cm||

Facing the Challenge 9 field free transitions in P(5/2) splits into ~30 intense  M J =  M F transitions, and numerous weaker  M J   M F transitions under applied electric field Fully resolved at voltage higher than 4000V/cm (impossible)

What to expect?  (X 2  5/2 )=1.60(7) D 1. Comparison with isovalent IrC 2. Electronegativity Si (8.15eV)<Ir (9.0eV) Possible to have small negative dipole moment Expect small positive dipole moment

Predicted spectra Stark spectra of IrSi 193 IrSi, P(5/2) 1754 V/cm|| LIF signal A B C,D c b a A B C D a b c

 (X 2  5/2 )= (6)D  ([16.0]1.5(v=6))=0.782(6)D  (X 2  5/2 )=+0.414(6)D  ([16.0]1.5(v=6))=-0.782(6)D Predicted spectra LIF signal

C (11.25eV) Si (8.15eV)Ir (9.0eV) Difference in bonding IrSi and IrC IrSi: Covalent bond IrC: Ionic bond

Compare with other Ir - containing molecule IrP IrCl IrO IrS Predict the reduced dipole moment of other Ir-containing molecule

Summary  Recorded high resolution LIF of the (6,0)[16.0]1.5 - X 2  5/2 bands for 191&193 IrSi  Analyzed, determined the fine and hyperfine parameters  Recorded & Analyzed Stark spectra to determine the molecular dipole moments for the X 2  5/2 and [16.0]1.5(v=6) states  Compared reduce dipole moment of other Ir-containing molecules with IrSi  Predict the reduced dipole moment of other Ir-containing molecule  High level relativistic calculations are in good agreement with observed dipole moment and eQq 0 (mag. hyperfine?)

Thank you DoE-BES Funding sources:  Prof. Michael Morse (University of Utah) –IrSi  Prof. John Stanton, Dr. Lan Cheng (U.Texas-Austin) -IrSi Collaborations:  Fang Wang  Ruohan Zhang Advisor: Prof. Timothy C. Steimle Group members:

Stark spectra of IrSi  (X 2  5/2 )= (64) D  ([16.0]1.5(v=6))=0.7821(63) D Determined dipole moments of IrSi Comparison Isovalent IrC  (X 2  5/2 )=1.60(7) D X 2  5/2 : 1  2 1  4 2  2 1  3 3  2 Why?  next slide