A simple, sensitive method of observing coherent multiphoton transitions by observation of subsequent photoionization is described.The method has been applied to a study of molecular iodine leading to two-photon excitation of a new Rydberg state of symmetry 1g with Te′ = 53 562.75 cm−1,Be′ = (0.04029) cm−1, and ωe′ = 241.41 cm−1.A theory for the process is outlined. A quantitative measure of the absolute intensity has been made. The ionization cross-section from the Rydberg level is ≤ 1.6 × 10−19 cm2.