Optical Zeeman Spectroscopy of Iron Monohydride, FeH Jinhai Chen, Timothy C. Steimle Department of Chemistry and Biochemistry, Arizona State University Zhong Wang, Trevor J. Sears Department of Chemistry, Brookhaven National Laboratory

Introduction The electronic spectrum of the FeH molecule is by far the most extensively studied of those for all of the diatomic 3d- transition metal hydrides. FeH has long been a molecule of interest to the astrophysical community and was first identified from features in the blue and green regions of the visible spectrum of the sun.  P. K. Carroll and P. McCormack, AstroPhys. J. Letts. 177, L33 (1972).

FIG. 1. The known and predicted low-lying electronic states of FeH below cm -1. Red lines indicate states accessed experimentally; these are at their empirically determined term values. The transitions indicated are those which have been investigated at high resolution in previous work. J. G. Phillips, S. P. Davis, B. Lindgren, and W. J. Balfour,AstroPhys. J. Suppl. Ser. 65, 721(1987) Previous Studies

Why measure the Zeeman effect ?  Solar spectra show the unusual rational line shapes.  It has been understood to be due to the local magnetic field in sunspots.  The FeH spectrum has been proposed as a probe for estimation of the magnetic fields in cooler stars and sub-stellar objects.

Our Work the Zeeman effect in a number of transitions involving low-J levels in the (1,0) band of the F 4 Δ i − X 4 Δ i band system (g-factors)

High Resolution Beam Spectroscopy Machine

High-resolution spectrometer Helmholtz coils

Results The Q(3.5) line in the (1,0) band of the F 4  7/2 – X 4  7/2 transition of FeH

Figure 2. The Q(3.5) line observed (A) field free; (B) in the presence of a magnetic field strength of 475 Gauss orientated perpendicular (ΔM J = ± 1) to the laser field. Figure 3. The Q(3.5) line observed (A) field free; (B) in the presence of a magnetic field strength of 530 Gauss orientated parallel (ΔM J = 0) to the laser field. ΔM J = ±1 ΔM J = 0 M I = ±0.5, ΔM I = 0

Analysis The matrix representation of H Z is diagonal in the projection quantum number M F, but of infinite dimension. The interaction with the static Zeeman field was modeled using the conventional Zeeman Hamiltonian: : the magnetic field vector; : the orbital momentum vector; : the spin momentum vector.

Non-parity Basis functions:  n  S  J  IFM F >  =  3/2,  2 &  =  7/2 H ij =Term value Modeling the Zeeman Effect (the eight Hund case (a  J )) Field-free Matrix H Zeeman H Zeeman = -  B (the twelve Hund case (a  J )) The (ν= 0) X 4 Δ 7/2 Laser Magnetic Resonance energy levels. J. M. Brown, H. Korsgen, S. P. Beaton, and K. M. Evenson, J. Chem. Phys. (2006), to be published.

The optimized values of g L is and the standard deviation of the fit was 24.5 MHz, which is commensurate with measurement uncertainly of spectral shifts. The g S was fixed to A non-linear least squares fitting procedure is used to optimize the values of g L for the (v =1)F 4  7/2 state.

(1)(2) Figure 3 The Q(3.5) line observed (lower) and predicted (upper) in the presence of a magnetic field of (1) 475 Gauss orientated perpendicular and (2) 530 Gauss orientated parallel of the laser field spectra.

Summary  The first laboratory measurements of the Zeeman splittings in the Q(3.5) line of the (1,0) band of the F 4  – X 4  transition of FeH have been modelled using a traditional effective Hamiltonian.  The upper-state g-factors obtained for the J = 3.5 level. The determined magnetic g L -factor is 1.079(8) when the g S -factor is constrained to  The determined parameters can be used to predict the magnetic tuning of features in this band in sunspot spectra. ( Work in progress)

Acknowledgement Thanks for your attention ! Steimle Group, Department of Chemistry & Biochemistry, Arizona State University (Thanks for Wilton Virgo and Tongmei Ma’s helps) Gas-phase Molecular Dynamics group, Department of Chemistry, Brookhaven National Laboratory, U.S. $$ National Science Foundation, Experimental Physical Chemistry Division. $$ Division of Chemical Sciences, Office of Basic Energy Sciences.

Electromagnet for Zeeman spectroscopy (56G-1.2kG) Mirror ‘‘MB,’’ molecular beam; ‘‘LB,’’ tunable laser radiation beam; ‘‘C,’’ Helmholtz coil; ‘‘IC,’’ iron core; ‘‘PMT,’’ cooled photomultiplier tube; ‘‘BPF,’’ band pass filter; ‘‘L,’’ lens; ‘‘M,’’ mirror.