Broadband transmission spectrum of an adenosine sample. Two shaded areas centered at 5.3 THz and 8 THz contain singularities caused by the TO phonons of the ZnTe and GaAs crystals, respectively. Arrows indicate vibrational modes at twenty frequencies (in units of THz) of 2.0, 2.2, 3.0, 3.4, 4.2, 4.5, 6.2, 6.7, 7.2, 8.6, 9.6, 10.5, 11.4, 12.4, 15.7, 16.2, 16.8, 17.7, 18.2, 19.2, with a frequency resolution of 0.075 THz. The insert shows the molecular structure of adenosine (C₁₀H₁₃N₅O₄). The red curve is a moving average of the transmission spectrum, as a guide to the eye.