Time dependence of the intensity (A), and the d-spacing (B) of the first order reflection of the rapidly formed H₂ phase referring to the experiment given in Figure 4.

The solid red line shows the best single exponential fit to the data. The time constant, k, was determined to be 0.10±0.03 and 0.12±0.02 sec⁻¹ for panels (A) and (B), respectively.