HIGH RESOLUTION LASER SPECTROSCOPY OF NICKEL MONOBORIDE, NiB E. Scott Goudreau, Colan Linton, Dennis W. Tokaryk Department of Physics and Centre for Laser, Atomic and Molecular Sciences, University of New Brunswick, Fredericton, NB, Canada Allan G. Adam Department of Chemistry and Centre for Laser, Atomic and Molecular Funding by NSERC

Previous work on NiB Theory: D.Tzeli and A. Mavridis(J. Chem. Phys. 128 (2008) 034309) Extensive calculation of molecular properties Predicted 2Σ+ ground state from π4σδ4 configuration Experiment: W. J. Balfour et al. (Chem. Phys. Lett. 463 (2008) 25-28) Pulsed laser medium resolution spectra of 2 electronic transitions Assigned as [19.7]2Σ+-X2Σ+ and [22.05]2Π- X2Σ+. J. Zhen et al. (Chin. J. Chem. Phys. 23 (2010) 626-629) Pulsed laser medium resolution spectra of a single electronic transition Assigned as [20.77]2Π3/2- X2Σ+. Need high resolution spectra to (a) examine fine and possibly hyperfine structure (b)resolve discrepancy in results of 2 above experiments

UNB Experiments Laser ablation source: Ni + B2H6 Pulsed Laser: Medium resolution (FWHM~0.3 cm-1) survey scans CW ring dye laser: High resolution (FWHM~0.006 cm-1) scans of strong bands

Low resolution (pulsed laser) spectrum Only Zhen et al. bands observed with significant intensity

2 – 0 Band (464nm) Band Heads 58Ni11B 60Ni11B

Assignments Picked out 4 main branches (2 R and 2 P) Rotational assignments of 2-0, 0-0, 3-0 bands of both isotopologues Fits very well as 2Σ+ - 2Σ+ transition Ground state: Regular 2Σ+ state . No distortion constants Small spin rotation constant γ = -0.0236 cm-1 Excited state required D and H distortion terms for rotational and fine structure, Very large spin-rotation γ = +0.8424 cm-1

Identity of Upper State? Assigned as 2Σ+ with unusually large γ Kopp and Hougen (Can. J. Phys. 45 (1967) 2581-2596) 2Σ state will fit equally well as a 2Π1/2 state 2Σ: Fine structure defined by spin-rotation constant γ splitting e and f levels of equal N 2Π1/2: Fine structure defined by Λ-doubling constant p splitting e and f levels of equal J p = γ – 2B

Upper State v=2 Energies 2Σ 2Π f e e f

Reduced term energy plots for upper state v=2 T – BN(N+1) T – B(J+1/2)2 2Σ 2Π1/2 γ – p = 1.0147cm-1 2B = 1.0147cm-1 γ = +0.8424cm-1 p = -0.1723cm-1 Label upper state as case (c) Ω = 0.5 state [20.6]0.5 Fine structure described by p parameter

R11 band-head region of 58Ni11B 2 – 0 band 9 1 N″ obs calc Partially resolved Hyperfine structure (11B I=3/2)

Magnetic Hyperfine Energies e-levels N=J-1/2 Case (b) 2Σ State f-levels N=J+1/2 C(J,F) = 0.5[F(F+1) – J(J+1) – I(I+1)] Case (a) 2Π state h = aΛ + (bF + 2c/3)Σ

Frosch and Foley Hyperfine Parameters a/Hz δi(r) = ψ2(0) Use to estimate boron atomic orbital in ground state configuration

Ground State Configuration X2Σ+ from π4σδ4 configuration Unpaired σ orbital primarily Ni(3dσ) + small contribution from B(2sσ? 2pσ?)? Observation of B hyperfine structure shows significant amount of B orbital Use atomic parameters to calculate molecular hyperfine parameters bF and c Morton and Preston (J. Magn. Reson. 30 (1978) 577-582 For Boron, <r-3> = 0.9293 a.u.-3 ψ2(0) = 1.775 a.u.-3 <3cos2θ – 1> = 0 for sσ and +4/5 for pσ

Hyperfine constants (cm-1) of the [20. 6]0 Hyperfine constants (cm-1) of the [20.6]0.5 v = 2 and X2Σ+ v = 0 states of 58Ni11B   h bF c [20.6]0.5 -0.0124(17) X2Σ+ (obs) 0.0067(8) 0.0063(17) X2Σ (calc sσ) 0.084 X2Σ (calc pσ) 0.0063 11B orbital contribution primarily 2pσ from ground B 2p 2P1/2 state!

Conclusions Zhen et al. transition reassigned as [20.6]0.5 – X2Σ+ Upper state is an Ω=0.5 state whose fine structure (ef parity splitting) is represented by the p (Ω-doubling) parameter Upper state requires 2nd and 3rd order distortion terms suggesting perturbation Observation and preliminary analysis of partially resolved 11B hyperfine structure shows that the σ orbital in the ground state has a small but significant contribution from B(2pσ) Need higher resolution experiments for a more complete analysis of hyperfine structure