Precision spectroscopy of high rotational states in H_2 investigated by Doppler-free two-photon laser spectroscopy in the EF^1\Sigma_g^+ - X^1\Sigma_g^+ system

TL;DR

This study extends high-precision Doppler-free two-photon spectroscopy of molecular hydrogen to highly excited rotational states, providing detailed level structure and testing quantum defect calculations for the EF^1Σ_g^+ state.

Contribution

It advances the understanding of H_2's high rotational states by combining experimental spectroscopy with quantum defect calculations for the first time.

Findings

Extended the known level structure of H_2 to high rotational states

Achieved unambiguous assignment of high-J levels using combination differences

Quantum defect calculations predicted levels within 5 cm^-1 accuracy

Abstract

Recently a high precision spectroscopic investigation of the EF^1\Sigma_g^+ - X^1\Sigma_g^+ system of molecular hydrogen was reported yielding information on QED and relativistic effects in a sequence of rotational quantum states in the X^1\Sigma^+_g$ ground state of the H_2 molecule [E.J. Salumbides et al., Phys. Rev. Lett. 107, 043005 (2011)]. The present paper presents a more detailed description of the methods and results. Furthermore, the paper serves as a stepping stone towards a continuation of the previous study by extending the known level structure of the EF^1\Sigma^+_g state to highly excited rovibrational levels through Doppler-free two photon spectroscopy. Based on combination differences between vibrational levels in the ground state, and between three rotational branches (O, Q and S branches) assignments of excited EF^1\Sigma^+_g levels, involving high vibrational and rotational quantum numbers, can be unambiguously made. For the higher EF^1\Sigma^+_g levels, where no combination differences are available, calculations were performed using the multi-channel quantum defect method, for a broad class of vibrational and rotational levels up to J=19. These predictions were used for assigning high-J EF-levels and are found to be accurate within 5 cm^-1.