Table 1.

Tentative band assignment for SERS spectra of caffeine, theobromine and paraxanthine

	Raman shift (cm−1)	Assignment
Caffeine and paraxanthine	509	N–C–C deformation (1)
	650	O=C–N deformation (1)
	693	C=O deformation (1)
	1006	N–CH3 asymmetric stretch (1)
	1247	C–N stretch (1)
	1450	δ(CH3) (2)
	1672	Unassigned
	2953	ν(CH3) (2)
Theobromine	637	δ(pyrimidine, imidazole ring) + δ(CH3) + ρ(CH3) (3)
	1228	δ(CH–N) + ρ(CH3) (3)
	1303	ν(C–N) + ρ(CH3) (2)
	1353	δ(CH–N) + ρ(CH3) (3)
	1413	δ(CH3) (3)
	1603	ν(C=C) + ν(C–N) + δ(CH3) (3)
	–
	2953	ν(CH3) (2)