Effect of molecular structural isomers in thermal lens spectroscopy

We explore the importance of molecular structure on thermal lens (TL) spectroscopy by measuring the effects of molecular isomerization on TL measurements. In particular, we present a case study for all the structural isomers of butanol, namely, normal-butanol (n-BuOH), secondary-butanol (s-BuOH), iso-butanol (i-BuOH) and tertiary-butanol (t-BuOH). We argue that the molecular isomerization influences the heat convection process in two possible ways: one being a change in the molecular surface area and the other being the steric hindrance. We show that n-BuOH has the highest capability to transfer heat by convection. Branching in the molecular structure renders the system sluggish as it makes the molecular motion successively retarded due to an increase in the mean free path. This we have defined as the molecular drift that slows under thermal conditions. In our studied isomers, therefore, t-BuOH drifts the slowest.