http://www.nat.vu.nl/~wimu/Publications/BSM-H2.pdf

Physics beyond the Standard Model from hydrogen spectroscopy

Weak transitions in the (2,0) overtone band of the hydrogen deuteride molecule at $\ensuremath{\lambda}=1.38\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ were measured in saturated absorption using the technique of noise-immune cavity-enhanced optical heterodyne molecular spectroscopy. Narrow Doppler-free lines were interrogated with a spectroscopy laser locked to a frequency comb laser referenced to an atomic clock to yield transition frequencies [$R(1)=217105181895(20)\text{ }\text{ }\mathrm{kHz}$; $R(2)=219042856621(28)\text{ }\text{ }\mathrm{kHz}$; $R(3)=220704304951(28)\text{ }\text{ }\mathrm{kHz}$] at three orders of magnitude improved accuracy. These benchmark values provide a test of QED in the smallest neutral molecule, and they open up an avenue to resolve the proton radius puzzle, as well as constrain putative fifth forces and extra dimensions.

Sub-Doppler Frequency Metrology in HD for Tests of Fundamental Physics.

A new 626-based Ames-2 PES refinement and Ames-2016 line lists for 13 CO2 isotopologues are reported. A consistent σRMS = ±0.02 cm−1 is established for hundreds of isotopologue band origins using the Ames-2 PES. Ames-2016 line lists are computed at 296 K, 1000 K and 4000 K using the Ames-2 PES and the same DMS-N2 dipole surface used previously, with J up to 150, E′ up to 24,000 cm−1 or 18,000 cm−1 and appropriate intensity cutoffs. The lists are compared to the CDSD-296, CDSD-4000 databases, UCL line lists, and a few recent highly accurate CO2 intensity measurements. Both agreements and discrepancies are discussed. Compared to the old Ames CO2 lists, the Ames-2016 line lists have line position deviations reduced by 50% or more, which consequently leads to more reliable intensities. The line shape parameters in the Ames-2016 line lists are predicted using the newly assigned conventional vibrational polyad quantum numbers for rovibrational levels below 12,000 cm−1 so the quality of the line shape parameters is similar to that of CDSD or HITRAN. This study further proves that a semi-empirically refined PES (Ames-1 and Ames-2) coupled with a high quality ab initio DMS (DMS-N2 and UCL) may generate IR predictions with consistent accuracy and is thus helpful in the analysis of laboratory spectra and simulations of various isotopologues. The Ames-2016 lists based on DMS-N2 have reached the ∼1% intensity prediction accuracy level for the recent 626 30013-00001 and 20013-00001 bands, but further quantification and improvements require sub-percent or sub-half-percent accurate experimental intensities. The inter-isotopologue consistency of the intensity prediction accuracies should have reached better than 1–3% for regular bands not affected by resonances. Since the Effective Dipole Models (EDM) in CDSD and HITRAN have 1–20% or even larger uncertainties, we show that the Ames lists can provide better alternative IR data for many hard-to-determine isotopologue bands. Comparison at 4000 K suggests that the Ames-4000 K 12C16O2 line list is reliable and consistent within the current cutoffs of J ≤ 150 and E′  ≤ 24,000 cm−1, but intensity contributions involving higher energy levels should not be omitted and future computations need to be converged up to at least 32,000 cm−1 or higher. The remaining issues are discussed regarding the source of energy level discrepancies, intensity underestimations by ∼50% for some weak bands, etc. and also future work.

Data for: Ames-2016 Line Lists for 13 Isotopologues of CO2: Updates, Consistency, and Remaining Issues

Experimental capabilities of molecular spectroscopy and its applications nowadays require a sub-percent or even sub-per mille accuracy of the representation of the shapes of molecular transitions. This implies the necessity of using more advanced line-shape models which are characterized by many more parameters than a simple Voigt profile. It is a great challenge for modern molecular spectral databases to store and maintain the extended set of line-shape parameters as well as their temperature dependences. It is even more challenging to reliably retrieve these parameters from experimental spectra over a large range of pressures and temperatures. In this paper we address this problem starting from the case of the H2 molecule for which the non-Voigt line-shape effects are exceptionally pronounced. For this purpose we reanalyzed the experimental data reported in the literature. In particular, we performed detailed line-shape analysis of high-quality spectra obtained with cavity-enhanced techniques. We also report the first high-quality cavity-enhanced measurement of the H2 fundamental vibrational mode. We develop a correction to the Hartmann–Tran profile (HTP) which adjusts the HTP to the particular model of the velocity-changing collisions. This allows the measured spectra to be better represented over a wide range of pressures. The problem of storing the HTP parameters in the HITRAN database together with their temperature dependences is also discussed.

The implementation of non-Voigt line profiles in the HITRAN database: H2 case study

Accurate investigations of quantum-level energies in molecular systems are shown to provide a testing ground to constrain the size of compactified extra dimensions. This is made possible by recent progress in precision metrology with ultrastable lasers on energy levels in neutral molecular hydrogen (H2, HD, and D2) and molecular hydrogen ions (H2+, HD+, and D2+). Comparisons between experiment and quantum electrodynamics calculations for these molecular systems can be interpreted in terms of probing large extra dimensions, under which conditions gravity will become much stronger. Molecules are a probe of spacetime geometry at typical distances where chemical bonds are effective (i.e., at length scales of an ?). Constraints on compactification radii for extra dimensions are derived within the Arkani-Hamed-Dimopoulos-Dvali framework, while constraints for curvature or brane separation are derived within the Randall-Sundrum framework. Based on the molecular spectroscopy of D2 molecules and HD+ ions, the compactification size for seven extra dimensions (in connection to M-theory defined in 11 dimensions) of equal size is shown to be limited to . While limits on compactification sizes of extra dimensions based on other branches of physics are compared, the prospect of further tightening constraints from the molecular method is discussed.

/pdf/constraints-on-extra-dimensions-from-precision-molecular-38lmjitjab.pdf

Constraints on extra dimensions from precision molecular spectroscopy

Cavity ring-down spectroscopy of the electric quadrupole transitions of H2 in the 784–852 nm region

The absorption spectrum of water vapor enriched in oxygen-17 has been recorded by a continuous-wave cavity ring-down spectrometer (CW-CRDS) at room temperature in the 12,277–12,894 cm−1 region. The typical sensitivity of 2 × 10−10 cm−1 allowed the detection of water vapor transitions with intensities larger than 1 × 10−28 cm−1/(molecule cm−2). In total, more than 3400 lines were observed in the recorded spectra with a typical frequency accuracy of 0.002 cm−1. In which more than 3400 transitions were ro-vibrationally assigned to five water isotopic species (H217O, H216O, H218O, HD16O, and HD17O) using the known empirical energy levels combined with the calculated variational line lists based on the results of Partridge and Schwenke. About 1300 transitions of H217O were assigned, leading to the determination of new energy levels of 17 vibration states. Those assigned H217O transitions are involved with the upper vibration states of (013), (023), (032), (051), (061), (070), (080), (090), (112), (131), (150), (160), (211), (230), (301), (310), and (320). The maximum values of the rotational numbers J and Ka were 16 and 9, respectively. The 5ν1 band of HD17O was assigned for the first time as well. The line positions and energy levels determined in this work were compared with literature, and it shows a significant improvement of the line positions of H217O and HD17O in the 12,277–12,894 cm−1 region.

CRDS absorption spectrum of 17O enriched water vapor in the 12,277–12,894 cm−1 range

Three bands 4003i–00001 (i=2, 3, 4) of the Fermi pentad of 12C16O2 near 830 nm have been recorded with a continuous-wave cavity ring down spectrometer. A sensitivity at the 5×10–11 cm−1 level allowed us to obtain line positions and intensities of these very weak bands. The measured line intensities of these three bands together with those published for the 10051–00001 and 10052–00001 bands were used to obtain the effective dipole moment parameters of 12C16O2 for the ΔP=17 series of transitions, where P=2V1+V2+3V3 is a polyad number (Vi (i=1, 2, 3) are vibrational quantum numbers). Comparisons of the measured line positions and intensities of the 4003i–00001 (i=2, 3, 4) bands to those from the AMES and GEISA line lists are given.

Cavity ring-down spectroscopy of CO2 overtone bands near 830 nm

Transitions of the 6ν3 overtone band of 14N216O near 775 nm have been studied by continuous-wave cavity ring-down spectroscopy. Line positions and intensities were derived from a fit of the line shape using a hard-collisional profile. The line positions determined with absolute accuracy of 5×10−4 cm−1 allowed us to reveal finer ro-vibrational couplings taking place after J>14 except a strong anharmonic interaction identified by the effective Hamiltonian model. The absolute line intensities have also been retrieved with an estimated accuracy of 2% for a majority of the unblended lines. A new set of ro-vibrational and dipole moment parameters were derived from the experimental values. A comparison between the line positions and intensities of the 6ν3 band obtained in this work and those from previous studies is given.

Xiao-qin Zhao

Papers

Cavity ring-down spectroscopy of the electric quadrupole transitions of H2 in the 784–852 nm region

CRDS absorption spectrum of 17O enriched water vapor in the 12,277–12,894 cm−1 range

Cavity ring-down spectroscopy of CO2 overtone bands near 830 nm

High Precision Cavity Ring Down Spectroscopy of 6ν3 Overtone Band of 14N216O near 775 nm