A molecular interaction study is carried out between the ionic liquid (IL) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate and 1-pentanol using the experimental values of density, speed of sound and refractive index measurements over the whole composition range as a function of temperature between (298.15 and 328.15) K at atmospheric pressure. The excess/deviation properties, such as molar volumes (V-m(E)), partial molar volumes ((V) over bar (E)(m)), partial molar volumes at infinite dilution ((V) over bar (E,infinity)(m)), isentropic compressibility (kappa(E)(s)), free length (L-f(E)), speeds of sound (u(E)), refractive index (Delta(phi)n(D)) and isobaric thermal expansion coefficient (alpha(E)(P)) obtained from the experimental values are fitted into the Redlich-Kister type equation to obtain the binary coefficients and the standard deviations. The negative values of excess properties such as V-m(E), kappa(E)(s), L-f(E), alpha(E)(P) and the positive values of u(E), Delta(phi)n(D) clearly indicated the existence of strong molecular interactions between the studied components. The values of (partial derivative V-m(E)/partial derivative T)(P) and (partial derivative H-m(E)/partial derivative P)(T) are also calculated to support the existing interactions. A quantitative analysis of these parameters is further supported by IR spectroscopic analysis. (C) 2016 Elsevier Ltd. All rights reserved.