Mass effect on rotational diffusion of small solutes in solution

► Prepare two pairs of solutes, CpM(CO)3 and M2(CO)10 (M = Mn, Re) in alkane solutions. ► Solutes in each pair have similar volume, solvent interactions, but different mass. ► Rotational correlation times of these solutes are determined by narrow-band IR pump broad-band IR probe spectroscopy. ► Heavier substitutions have larger rotational correlation times. ► Mass effect on rotational correlation times is discussed.