Speaker: Kenneth Lai, Vrije Universiteit Amsterdam
Program Description:
Molecular hydrogen is one of the benchmark molecules for testing molecular quantum mechanics due to its simplicity as a particle system. Most of the precision measurements on molecular hydrogen focus on the low vibrational levels (v <= 3). The level energies of these states are not sensitive to the potential energy curve at large internuclear distance. Precision measurements on vibrationally excited molecular hydrogen help test the ground electronic state potential curve over large internuclear distance.
The photolysis of H2S at 281.8 nm has been shown to be an “efficient” method to produce ro-vibrationally excited H2 in the ground electronic state [1-3]. The highest vibrational levels v = 14 and some quasi-bound resonances of H2 with μs-lifetime (v, J) = (7,21), (8,19), (9,17) and (10,15) are identified and probed through Doppler-free two photon spectroscopy of F 1Σg+ - X 1Σg+ transitions. Transition frequencies were determined with an uncertainty down to 30 MHz. The energy splittings in ground electronic state are determined from the combination difference of F-X transition frequencies and compared with ab initio calculations, including relativistic and QED effects. This study extends precision test of QED theory for the electronic ground state of the hydrogen molecule to the very highest bound level, and into the quasi-bound region.
Vibrationally excited HD and D2 are produced and probed using the similar scheme. Due to the isotopic shift and smaller zero-point energy for HDS and D2S, the dissociation energies are higher than H2S. Photolysis of D2S at 281.8 nm is expected to be marginally enough to produce all bound levels of D2. In the preliminary measurement, vibrationally excited and even some quasibound resonances of HD and D2 are observed from the photolysis fragment.
[1] K.-F. Lai, M. Beyer, E. J. Salumbides, and W. Ubachs, J. Phys. Chem. A, vol. 125, pp. 1221–1228, 2021
[2] K.-F. Lai, M. Beyer, E. J. Salumbides, and W. Ubachs, Phys. Rev. Lett., vol. 127, p. 183001, 2021
[3] K.-F. Lai, E. J. Salumbides, M. Beyer, and W. Ubachs, Mol. Phys., p. e2018063, 2021
