  New spatially scanned spectropolarimetry sunspot observations are made of
photospheric atomic and molecular absorption lines near 4135nm. The relative
splittings among several atomic lines are measured and shown to agree with
values calculated with configuration interaction and intermediate coupling.
Large splitting is seen in a line identified with Fe I at 4137nm, showing
multiple Stokes V components and an unusual linear polarization. This line will
be a sensitive probe of quiet Sun magnetic fields, with a magnetic sensitivity
of 2.5 times larger than that of the well-known 1565nm Fe I line.
