ANH LE AND TIMOTHY C. STEIMLE, Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287; LAN CHENG AND JOHN F. STANTON, The University of Texas at Austin, Austin, TX 78712-0165.

The optical spectrum of iridium monosilicide (IrSi) was recently observed using REMPI spectroscopy in the range 17200 to 23850 cm-1 . The observation was supported by an ab initio calculation which predicted a X 2 Delta5/2 state. Here, we report on the analysis of the optical Stark effect for the X 2 Delta5/2 and [16.0]1.5 (v=6) states. The (6,0)[16.0]1.5 - X 2 Delta5/2 and the (7,0)[16.0]3.5- X 2 Delta5/2 bands of IrSi have been recorded using high-resolution laser-induced fluorescence spectroscopy. The observed optical Stark shifts for the 193IrSi and 191IrSi isotopologues were analyzed to produce the electric dipole moments of -0.4139(64)D and 0.7821(63)D for the X 2 Delta5/2 and [16.0]1.5 (v=6) states, respectively. The negative sign of electric dipole moment of the X 2 Delta5/2 state is supported by high-level quantum-chemical calculations employing all-electron scalar-relativistic CCSD(T) method augmented with spin-orbit corrections as well as corrections due to full triple excitations. In particular, electron-correlation effects have been shown to be essential in the prediction of the negative sign of the dipole moment. A comparison with other iridium containing molecules will be made.