In this article, we quest for understanding the temperature dependent optical modes present in a-GexAs35-xSe65 thin films. Strikingly, temperature dependent Raman spectra provide direct evidence of softening of AsSe3/2 pyramidal units and Se clusters at higher temperatures. In a stark contrast, GeSe4/2 corner and edge sharing tetrahedral units remain rigid against the temperature variation. Subsequently, FIR measurements at room temperature also provide significant insights on the optical modes in consistent with Raman data. In addition to that, our experimental results present fascinating optical features-thermally and compositionally tunable optical absorption spectra. We found that structural and optical parameters are closely related and help us in understanding the various physico-chemical properties which can eventually contribute to the field of optics and optoelectronics. (C) 2016 Published by Elsevier B.V.