1. HIGH FREQUENCY EPR

2. Energy level diagram for D < 0 system B // z-axis of molecule Note frequency range

3. Cavity perturbation Cylindrical TE01n (Q ~ 10 4 - 10 5 ) f = 16  250 GHz Single crystal 0.2×0.2×0.1 mm 3 T = 0.5 to 300 K, B up to 45 tesla M. Mola et al., Rev. Sci. Inst. 71, 186 (2000) 

4. More on the technique We use a Millimeter-wave Vector Network Analyzer (MVNA, ABmm) as a spectrometer.We use a Millimeter-wave Vector Network Analyzer (MVNA, ABmm) as a spectrometer. This device allows vector measurements with continuous frequency coverage from 8 to 600 GHz.This device allows vector measurements with continuous frequency coverage from 8 to 600 GHz. We currently use cavities up to 250 GHz and have a reflectivity probe working up to 450 GHz.We currently use cavities up to 250 GHz and have a reflectivity probe working up to 450 GHz. We use over-moded cavities when closely spaced frequencies are required.We use over-moded cavities when closely spaced frequencies are required. A 3 He capability has just been successfully tested.A 3 He capability has just been successfully tested. The cavity technique, in combination with the vector capability, is extremely important for line shape analysis; eliminates many instrumental effects which plague single-pass scalar measurements.The cavity technique, in combination with the vector capability, is extremely important for line shape analysis; eliminates many instrumental effects which plague single-pass scalar measurements. S. Hill, S. Maccagnano, K. Park, R. M. Achey, J. M. North and N. S. Dalal, Phys. Rev. B 65, 224410 (2002).S. Hill, S. Maccagnano, K. Park, R. M. Achey, J. M. North and N. S. Dalal, Phys. Rev. B 65, 224410 (2002). M. Mola et al., Rev. Sci. Inst. 71, 186 (2000).M. Mola et al., Rev. Sci. Inst. 71, 186 (2000).

5. Energy level diagram for S = 9 / 2, D < 0 system B // z-axis of molecule

6. HFEPR for high symmetry (C 3v ) Mn 4 cubane Field // z-axis of the molecule (±0.2 o ) Inhomogeneous lineshape

7. Fit to easy axis data - yields diagonal crystal field terms

8. 0 1 2 3 4 5 6 7 -30-20 -10 0 10 20 30 D = -0.530 cm E = B 2 2 = 0.0206 cm Magnetic field (tesla) Frequency (GHz) Energy level diagram for B  z-axis

9. Hard axis data for C 3v Mn 4 cubane

10. Fit to hard axis data - sensitive to transverse crystal field terms For this cubane, no direct shifts in the spectra could be detected and attributed to transverse crystal field terms

11. Fit to hard axis data for a Ni 4 cubane - [Ni(hmp)(tBuEtOH)Cl] 4 There are actually two species of Ni 4 cluster in this crystal structure, due to two distinct crystallographic sites 101 GHz, hard plane rotation