Identifying Quantum Tunneling at Ambient Temperature through Rate-Driving Force Responsiveness.

Quantum mechanical tunneling can strongly influence chemical reactivity, yet its experimental identification remains limited. Here we derive a new diagnostic principle: tunneling leaves a distinct signature in the rate-driving force relationship. We show that tunneling reshapes the scaling relationship between reaction rate and driving force. Within a Hammond-type interpolation of barrier topology, over-the-barrier reactivity primarily translates the interpolated change in barrier height into rate-driving-force responsiveness. When through-barrier transmission contributes, the interpolated change in barrier width is also expressed in the rate response, producing significantly enhanced responsiveness. This principle enables a simple experimentally anchored diagnostic for tunneling based on responsiveness analysis within a reaction family, complementing existing diagnostics that often rely on cryogenic temperatures or isotopic substitution. We demonstrate the principle using the syn elimination of selenoxides as a benchmark model system at room temperature. Because this diagnostic principle relies only on standard kinetic measurements, it should be broadly applicable to reactions with measurable elementary kinetics.