We report mid-IR wavelength observations toward the low mass star form
ing region IRAS 16293-2422 between 45 mu m - 197 mu m with the Long Wa
velength Spectrometer (LWS) on board ISO, and of the CI(609 mu m) line
observed with the JCMT. A map of the CII(157 mu m) line shows that th
e region is relatively uncontaminated by Photo-Dissociation Region-lik
e emission; there is only weak diffuse CII emission, which results fro
m the illumination of the cloud by a faint UV field (G(o) similar to 6
). The observed CI(609 mu m) line intensity and narrow profile is cons
istent with this interpretation. On-source, the LWS detected the OI(63
mu m) and several molecular lines. In this work we report and discuss
in detail the lines which dominate the 43 mu m - 197 mu m spectrum, n
amely CO, H2O and OH rotational lines and the OI(63 mu m) fine-structu
re line. Combining the CO J(up)=14 to 25 observations with previous J(
up)=6 measurements, we derive stringent limits on the density (similar
to 3 . 10(4)cm(-3)), temperature (similar to 1500 K), and column dens
ity (similar to 1.5 . 10(20)cm(-2)) of the emitting gas. We show that
this warm gas is associated with the outflow and that a low velocity,
C-type shock can account for the characteristics of the CO spectrum. I
f the observed H2O and OH lines originate in the same region where the
CO lines originate, the H2O and OH abundance derived from the observe
d lines is [H2O] / [H-2] similar to 2.10(-5) and [OH] / [H-2] similar
to 5.10(-6) respectively. Given the relatively high temperature of the
emitting gas, standard chemistry would predict all the gas-phase oxyg
en to be in water. The relatively low water abundance we observed may
mean either that most of the oxygen is locked into grains or that the
time scale required to convert the gas-phase oxygen into water is high
er that the outflow time scale, or both. The relatively high abundance
of OH with respect to H2O gives support to the latter hypothesis. Fin
ally, we speculate that the OI(63 mu m) line emission originates in th
e collapsing envelope that surrounds the central object. The successfu
l comparison of the observed flux with model predictions of collapsing
envelopes gives a mass accretion rate toward the central object great
er than or equal to 3.10(-5)M. yr(-1) and an accretion shock radius la
rger than three times the protostar radius.