  We present the results of a 7 mm spectral survey of molecular absorption
lines originating in the disk of a z=0.89 spiral galaxy located in front of the
quasar PKS 1830-211. [...] A total of 28 different species, plus 8 isotopic
variants, were detected toward the south-west absorption region, located about
2 kpc from the center of the z=0.89 galaxy, which therefore has the largest
number of detected molecular species of any extragalactic object so far. The
results of our rotation diagram analysis show that the rotation temperatures
are close to the cosmic microwave background temperature of 5.14 K that we
expect to measure at z=0.89, whereas the kinetic temperature is one order of
magnitude higher, indicating that the gas is subthermally excited. The
molecular fractional abundances are found to be in-between those in typical
Galactic diffuse and translucent clouds, and clearly deviate from those
observed in the dark cloud TMC 1 or in the Galactic center giant molecular
cloud Sgr B2. The isotopic ratios of carbon, nitrogen, oxygen, and silicon
deviate significantly from the solar values, which can be linked to the young
age of the z=0.89 galaxy and a release of nucleosynthesis products dominated by
massive stars. [...] We also report the discovery of several new absorption
components, with velocities spanning between -300 and +170 km/s. Finally, the
line centroids of several species (e.g., CH3OH, NH3) are found to be
significantly offset from the average velocity. If caused by a variation in the
proton-to-electron mass ratio mu with redshift, these offsets yield an upper
limit |Delta_mu/mu|<4e-6, which takes into account the kinematical noise
produced by the velocity dispersion measured from a large number of molecular
species.
