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Submillimeter lines of CN, NO, CO+ and SO+, and upper limits on SH+ and N2Oare observed with the James Clerk Maxwell Telescope in two high-mass and up tonine low-mass young stellar objects and compared with chemical models. Constantfractional abundances derived from radiative transfer modeling of the linestrengths are x(CN) ~ a few x 10^{-11}-10^{-8}, x(NO) ~ 10^{-9}-10^{-8} andx(CO+) ~ 10^{-12}-10^{-10}. SO+ has abundances of a few x 10^{-11} in thehigh-mass objects and upper limits of ~ 10^{-12}-10^{-11} in the low-masssources. All abundances are up to 1-2 orders of magnitude higher if themolecular emission is assumed to originate mainly from the inner region (< 1000AU) of the envelope. For high-mass sources, the CN, SO+ and CO+ abundances andabundance ratios are best explained by an enhanced far-ultraviolet (FUV) fieldimpacting gas at temperatures of a few hundred K. The observed column densitiesrequire that this region of enhanced FUV has scales comparable to the observingbeam, such as in a geometry in which the enhanced FUV irradiates outflow walls.For low-mass sources, the required temperatures within the FUV models of T >300 K are much higher than found in models, so that an X-ray enhanced regionclose to the protostar (r < 500 AU) is more plausible. The observed abundancesimply X-ray fluxes for the Class 0 objects of L_X ~ 10^{29}-10^{31} erg s^{-1},comparable to those observed from low-mass Class I protostars. Spatiallyresolved data are needed to clearly distinguish the effects of FUV and X-raysfor individual species.Comment: accepted by A&A (02/01/2007

Tracing high energy radiation with molecular lines near deeply embedded protostars