A study of absorption features in the 3 micron spectra of molecular cloud sources with H2O ice bands

New 3.3-3.6 mu m spectra were obtained of nine young stellar objects embedded in molecular clouds. An absorption feature at similar to 3.47 mu m (2880 cm(-1)) with FWHM similar to 0.09 mu m (80 cm(-1)), first identified by Allamandola et al. (1992), was definitively detected toward seven objects, and marginally in the other two. The feature is better correlated with H2O ice than with the silicate dust optical depth in the data obtained to date. Assuming the feature is due to a C-H stretch absorption, the abundance of the C-H bonds averaged along the lines of sight is closely related to that of H2O ice. We interpret the correlation with H2O ice as indicating that the C-H bonds form together with H2O ice on grain surfaces in the molecular clouds, though other formation mechanisms are not ruled out. A second absorption feature at 3.25 mu m (3080 cm(-1)) was detected toward NGC 7538/IRS 1 and S140/IRS 1; this feature was first detected in spectra of Mon R2/IRS 3 (Sellgren, Smith, & Brooke 1994; Sellgren et al. 1995). There is as yet insufficient data to tell whether this feature is better correlated with H2O ice or silicates.