Precision measurements and test of molecular theory in highly-excited vibrational states of H$_2$ $(v=11)$

TL;DR

This study precisely measured vibrational transition energies in molecular hydrogen at v=11, confirming advanced theoretical models with unprecedented accuracy using Doppler-free two-photon spectroscopy and autoionizing Rydberg states.

Contribution

The paper presents highly accurate experimental transition energies for H₂ in a highly excited vibrational state, improving detection methods and validating advanced ab initio molecular theories.

Findings

Transition energies measured with 45 MHz accuracy.

Experimental results agree with and surpass theoretical calculations.

Enhanced detection efficiency via autoionizing Rydberg states.

Abstract

Accurate $EF{}^1\Sigma^+_g-X{}^1\Sigma^+_g$ transition energies in molecular hydrogen were determined for transitions originating from levels with highly-excited vibrational quantum number, $v=11$, in the ground electronic state. Doppler-free two-photon spectroscopy was applied on vibrationally excited H$_2^*$, produced via the photodissociation of H$_2$S, yielding transition frequencies with accuracies of $45$ MHz or $0.0015$ cm$^{-1}$. An important improvement is the enhanced detection efficiency by resonant excitation to autoionizing $7p\pi$ electronic Rydberg states, resulting in narrow transitions due to reduced ac-Stark effects. Using known $EF$ level energies, the level energies of $X(v=11, J=1,3-5)$ states are derived with accuracies of typically 0.002 cm$^{-1}$. These experimental values are in excellent agreement with, and are more accurate than the results obtained from the most advanced ab initio molecular theory calculations including relativistic and QED contributions.