THE 3.2-3.6 MICRON SPECTRA OF MONOCEROS R2/IRS-3 AND ELIAS-16

We have obtained 3.2-3.6 mum spectra, with a resolution lambda/DELTAlambda approximately 750, of the protostar Mon R2/IRS-3 and of Elias 16, a background K giant behind the Taurus molecular cloud. A feature at 3.482 mum (2872 cm-1), with a full width at half-maximum of 0.09 mum (76 cm-1), is clearly seen in Mon R2/IRS-3. This feature is not detected in Elias 16. The 3.482 mum feature in Mon R2/IRS-3 is similar to a feature at 3.466-3.478 mum (2875-2885 cm-1) detected by Allamandola et al. in four protostars and attributed by these authors to a CH stretch in hydrocarbons dominated by sp3-bonded carbon. Neither Mon R2/IRS-3 nor Elias 16 shows absorption at 3.540 mum (2825 cm-1), which has been detected in two of the four protostars observed by Allamandola et al. and attributed by them to CH3OH ice. Our limit on CH3OH ice toward Elias 16 is compared to models of gas-grain chemistry in dark clouds. Our results confirm those of Allamandola et al. that at this resolution the 3.4 mum absorption due to dust in molecular clouds has very different spectral structure than that due to dust in the diffuse interstellar medium.