A modified Sell‐type ultrasonic transducer, utilizing Teflon materials and the hard‐anodization process for the aluminum back plates, shows significant improvement in operating characteristics over earlier models. The vibrational self‐relaxation times of ClCN ( pτ=29 ns bar) and BrCN ( pτ=15 ns bar) are measured for the first time. The results are discussed in relation to the empirical Lambert–Salter plot for V–R,T energy transfer.