() Define the depth of penetration (dp) in Attenuated Total Reflection (ATR) and provide the dp in the increasing order (when only one parameter is changing; note that just order is required with brief justification and not the specific values for the depth of penetration) for: (1) ATR crystals: Si, Ge and diamond; (2) Samples: X with refractive index 1.55 and Y with refractive index 1.45 (3) absorption bands at 800 cm-1 and 1400 cm-1 (4) angles of incidence of 45 and 60. [8 marks]