Molecular line surveys and fully sampled spectral line maps at 1.3 and 0.87 mm are used to examine the
physical and chemical characteristics of the extreme Class I sources IRAS 4A and 4B in the L1450/NGC 1333
molecular cloud complex. A very well collimated, jetlike molecular outflow emanates from IRAS 4A, with a
dynamical age of a few thousand years. Symmetric, clumpy structure along the outflow lobes suggests that
there is considerable variability in the mass-loss rate or wind velocity even at this young age. Molecular emission
lines toward IRAS 4A and 4B are observed to be weak in the velocity range corresponding to quiescent
material surrounding the young stellar objects (YSOs). Depletion factors of 10-20 are observed for αll molecules,
including CO, even for very conservative mass estimates from the measured millimeter and submillimeter
dust continuum. However, abundances scaled with respect to CO are similar to other dark
molecular cloud cores. Such depletions could be mimicked by high dust optical depths or increased grain
emissivities at the observing frequencies of 230 and 345 GHz, but the millimeter and submillimeter spectral
energy distributions suggest that this is unlikely over the single-dish size scales of 5000-10,000 AU.
Dense, outflowing gas is found to be kinematically, but not spatially, distinct from the quiescent material on
these size scales. If CO is used as a chemical standard for the high-velocity gas, we find substantial enhancements
in the abundances of several molecules in outflowing material, most notably CS, SiO, and CH_30H. The
SiO emission is kinematically well displaced from the bulk cloud velocity and likely arises from directly
shocked material. As is the case for CO, however, the outflow features from more volatile species are centered
near the cloud velocity and are often characterized by quite low rotational temperatures. We suggest that
grain-grain collisions induced by velocity shear zones surrounding the outflow axes transiently desorb the
grain mantles, resulting in large abundance enhancements of selected species. Similar results have recently
been obtained in several other low-mass YSOs, where the outflowing gas is often both kinematically and spatially
distinct, and are illustrative of the ability of accretion and outflow processes to simultaneously modify
the composition of the gas and dust surrounding young stars
