  We present high-resolution spectroscopic observations of GRB060418, obtained
with VLT/UVES. These observations were triggered using the VLT Rapid Response
Mode (RRM), which allows for automated observations of transient phenomena,
without any human intervention. This resulted in the first UVES exposure of
GRB060418 to be started only 10 minutes after the initial Swift satellite
trigger. A sequence of spectra covering 330-670 nm were acquired at 11, 16, 25,
41 and 71 minutes (mid-exposure) after the trigger, with a resolving power of 7
km/s, and a signal-to-noise ratio of 10-15. This time-series clearly shows
evidence for time variability of allowed transitions involving FeII
fine-structure levels, and metastable levels of both FeII and NiII, at the
host-galaxy redshift z=1.490. This is the first report of absorption lines
arising from metastable levels of FeII and NiII along any GRB sightline. We
model the observed evolution of the level populations with three different
excitation mechanisms: collisions, excitation by infra-red photons, and
fluorescence following excitation by ultraviolet photons. Our data allow us to
reject the collisional and IR excitation scenarios with high confidence. The UV
pumping model, in which the GRB afterglow UV photons excite a cloud of atoms
with a column density N, distance d, and Doppler broadening parameter b,
provides an excellent fit, with best-fit values: log N(FeII)=14.75+0.06-0.04,
log N(NiII)=13.84+/-0.02, d=1.7+/-0.2 kpc (but see Appendix A), and b=25+/-3
km/s. The success of our UV pumping modeling implies that no significant amount
of FeII or NiII is present at distances smaller than ~1.7 kpc (but see erratum
in Appendix A), most likely because it is ionized by the GRB X-ray/UV flash.
Because neutral hydrogen is more easily ionized than FeII and NiII, this
minimum distance also applies to any HI present. [abridged]
