The hydrogen molecular ion H2+, constituted of two protons and an electron, is the simplest molecule. Owing to its simple three-body structure, the energy level structure of the hydrogen molecular ion can be calculated with high accuracy and precision. Transition frequencies between vibrational levels in the ground electronic state of H2+ can be calculated with uncertainties in the parts-per-trillion level . Such ab initio calculations of energy level structure in molecules include contributions from non-relativistic quantum mechanics, quantum electrodynamics and nuclear finite-size effects. A measurement of vibrational transition frequencies in hydrogen molecular ion with accuracy and precision higher than that of theory would then provide a stringent test of molecular theory. Moreover, experimental and theoretical results can be combined to extract the values of various physical constants, such as the proton-electron mass ratio [2, 3]. Comparison between theory and experiment may also allow search for physics beyond the Standard Model of particle physics . In this presentation, I will describe an experiment aimed to measure the frequency of a vibrational transition of the deuterated hydrogen molecular ion HD+ with an uncertainty better than that of theory, and subsequently extract a value of the proton-electron mass ratio more precise than its existing best determination . I will discuss the motivation, methods and briefly state the recent results from this experiment.
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