Determination of the Interval between the Ground States of Para- and Ortho- H2

Abstract

Nuclear-spin-symmetry conservation makes the observation of transitions between quantum states of ortho-and para-H 2 extremely challenging. Consequently, the energy-level structure of H 2 derived from experiment consists of two disjoint sets of level energies, one for para-H 2 and the other for ortho-H 2. We use a new measurement of the ionization energy of para-H 2 [E I ðH 2 Þ=ðhcÞ ¼ 124 417.491 098ð31Þ cm −1 ] to determine the energy separation [118.486 770ð50Þ cm −1 ] between the ground states of para-and ortho-H 2 and thus link the energy-level structure of the two nuclear-spin isomers of this fundamental molecule. Comparison with recent theoretical results [M. Puchalski et al., Phys. Rev. Lett. 122, 103003 (2019)] enables the derivation of an upper bound of 1.5 MHz for a hypothetical global shift of the energylevel structure of ortho-H 2 with respect to that of para-H 2 .

Reactions of H2, HD, and D2 with H2+, HD+, and D2+: Product-Channel Branching Ratios and Simple Models

“…Typical values for these rate coefficients used to model the chemical composition of cold, low-density plasmas from ref ( 10 ) are listed in the last column of Table 1 . The remaining columns of Table 1 provide values of the 0 K reaction energies for these reactions (Δ i U (0 K)) and for the corresponding charge-transfer reactions (Δ i ,CT U (0 K)), which we have derived from literature values of the dissociation and ionization energies of H 2 , 27 , 28 HD, 29 and D 2 , 30 the dissociation energy of H 2 + , 31 the ionization energies of H 32 and D, 33 the dissociation energy of H 3 + , 34 and the zero-point energies of H 3 + , H 2 D + , HD 2 + , and D 3 + . 35…”

Precision Measurements in Few-Electron Molecules: The Ionization Energy of Metastable He42 and the First Rotational Interval of Semeria1, Jansen2, Camenisch3 et al. 2020Phys. Rev. Lett.

“…The MQDT parameters of triplet np and nf Rydberg states determined by Sprecher et al [36] were employed without change. In order to ensure the robust extrapolation of ionization energies, we adopt the approach of Beyer et al [37]. The experimental dataset used for the extrapolation is chosen so as to cover an energy range at least as large as the energy interval to be extrapolated.…”

Precision measurement of quasi-bound resonances in H$_2$ and the H + H scattering length

“…Potential energy curves for the X 1 Σ + g ground state and the EF 1 Σ + g excited states, drawn for the J = 0 rotationless energies and for higher odd J values, including the centrifugal energy. Also wave functions for a bound X (7,19) and quasi-bound X (8,19) * level are displayed. The wave function for the F0(J = 19) excited level (upper panel) indicates overlap at large internuclear separation (4-5 a.u.…”

“…The assignment of the F0-X transitions originating in quasi-bound resonances is based on a comparison with computed level separations between X 1 Σ + g and F 1 Σ + g levels as presented in section III. To obtain the excitation energies of H * 2 above X 1 Σ + g (v = 0, J = 0) the values for the binding energies of X(v, J) are augmented with the value for the dissociation energy of H 2 , for which the most recent experimental value was taken, D 0 = 36118.069605(31) cm −1 [19], which is in excellent agreement with the theoretical value of D 0 = 36118.069632 (26) cm −1 [12]. From a combination of these values, included in Table II, a prediction can be made for the F0-X transitions probing the quasi-bound resonances.…”

“…Progress on the theoretical side was matched by increasingly precise measurements of the dissociation energy of the smallest neutral molecule [13][14][15][16][17][18][19][20], now finding agreement between theory and experiment at the level of 10 −5 cm −1 . The computations were verified via comparison with measurements of high-rotational angular momentum states [21] and vibrational splittings in H 2 [22][23][24][25][26].…”