Embedded Protostars in the Dust, Ice, and Gas In Time (DIGIT) Key
  Program: Continuum SEDs, and an Inventory of Characteristic Far-Infrared
  Lines from PACS Spectroscopy
  We present 50-210 um spectral scans of 30 Class 0/I protostellar sources,
obtained with Herschel-PACS, and 0.5-1000 um SEDs, as part of the Dust, Ice,
and Gas in Time (DIGIT) Key Program. Some sources exhibit up to 75 H2O lines
ranging in excitation energy from 100-2000 K, 12 transitions of OH, and CO
rotational lines ranging from J=14-13 up to J=40-39. [O I] is detected in all
but one source in the entire sample; among the sources with detectable [O I]
are two Very Low Luminosity Objects (VeLLOs). The mean 63/145 um [O I] flux
ratio is 17.2 +/- 9.2. The [O I] 63 um line correlates with Lbol, but not with
the time-averaged outflow rate derived from low-J CO maps. [C II] emission is
in general not local to the source. The sample Lbol increased by 1.25 (1.06)
and Tbol decreased to 0.96 (0.96) of mean (median) values with the inclusion of
the Herschel data. Most CO rotational diagrams are characterized by two
optically thin components (<N> = (0.70 +/- 1.12) x 10^49 total particles). N_CO
correlates strongly with Lbol, but neither Trot nor N_CO(warm)/N_CO(hot)
correlates with Lbol, suggesting that the total excited gas is related to the
current source luminosity, but that the excitation is primarily determined by
the physics of the interaction (e.g., UV- heating/shocks). Rotational
temperatures for H2O (<Trot> = 194 +/- 85 K) and OH (<Trot> = 183 +/- 117 K)
are generally lower than for CO, and much of the scatter in the observations
about the best fit is attributed to differences in excitation conditions and
optical depths amongst the detected lines.
