These peaks come from C-H stretching modes within the polyethylene support itself. Polyethylene is composed of repeating -CH2-CH2- units; the C-H bonds within this structure absorb in the IR region, giving rise to the two spikes mentioned. Solution These peaks come from C-H stretching modes within the polyethylene support itself. Polyethylene is composed of repeating -CH2-CH2- units; the C-H bonds within this structure absorb in the IR region, giving rise to the two spikes mentioned..