Comment on "Computational evidence for sulfur atom tunneling in the ring flipping reaction of S4N4".

• Sulfur atom tunneling in the S 4 N 4 ring flipping reaction is impossible. • Not only the mass, but also the barrier width and height are critical for tunneling. • Beyond second row elements, the mass and/or the barrier width makes tunneling close to impossible. • Caution must be exercised when predicting experimentally observable reactions. In a recent article (Chem. Phys. Lett. 749 (2020), 137440), Kumar and Mallick predict by computations that a sulfur atom tunneling mechanism leads to a ring flipping reaction of S 4 N 4 below 70 K. Herein, on the basis of their tunneling computations, it is shown that the sulfur atom tunneling is not viable, and therefore impossible to be probed experimentally. Based on this, we discuss the prerequisites for a chemical reaction to be driven by heavy atom tunneling. [ABSTRACT FROM AUTHOR]