High-precision Ramsey-comb spectroscopy on molecular deuterium for tests of molecular quantum theory

Precision spectroscopy of simple, calculable molecules has become an important tool to compare experiments with theory in effort test our understanding the fundamental laws physics. For this purpose, we have measured EF1Σg+(v′=0,N′=0)←X1Σg+(v″=0,N″=0) transition frequency molecular deuterium (D2) unprecedented accuracy. We use Ramsey-Comb at deep-ultraviolet wavelengths (201 nm) a two-photon, Doppler-free interrogation scheme. The resulting is f=2,981,779,227,578(19) kHz. 1-σ uncertainty 19 kHz represents improvement more than two orders magnitude compared best previous measurement. In paper, give extensive description methods and experimental apparatus that employed. Particular attention given aspects recently improved, such as comb laser system, method signal recording, cryogenic D2 beam apparatus. combination future measurements ionisation energy EF state, measurement paves way for improved determination ground state dissociation deuterium.