Laboratory identification of the emission features near 3.5 microns in the pre-main sequence star HD 97048

This paper presents the results of a laboratory study of formaldehyde (H2CO) suspended in low temperature molecular matrices with compositions similar to what may be found in the 'dirty ice' mantles of grains. It is shown that the emission features near 3.5 microns in the pre-main-sequence star HD 97048 can be matched by a mixture of chemical complexes of H2CO with surrounding molecules in the grain. Furthermore, a discussion is presented of various possible excitation mechanisms for this emission. The conclusion is, that for the features near 3.5 microns in HD 97048, UV pumped IR fluorescence is the most likely mechanism.