Accurate deuterium spectroscopy for fundamental studies

Abstract

• weak quadrupole S(2) 2-0 line in self-perturbed D2 is measured • collisional line-shape effects and energy of this rovibrational transition are calculated • the velocity-changing collisions are handled with the hardsphere collisional kernel • the experimental and theoretical pressure broadening and shift are consistent within 5 • we observe 3.4 sigma discrepancy between experimental and theoretical line position

Testing the ab initio quantum‐scattering calculations for the D2–He benchmark system with stimulated Raman spectroscopy

“…This can be clearly seen when the strength of the speed dependence of the shift is expressed quantitatively and compared with the real part of the frequency of the optical velocity‐changing collisions . Within the quadratic approximation of the speed dependence its strength can be expressed as For the D 2 S 0 (0) line considered here, at T =77 K and p =1 atm, Δ 2 =0.26·10 −3 cm −1 , which is more than two orders of magnitude smaller than cm −1 . The width of the additional asymmetric inhomogeneous broadening originating from the speed dependence of collisional shift within the quadratic approximation can be expressed with a simple analytical formula For the D 2 S 0 (0) line, this additional broadening is Γ δ =0.0016·10 −3 cm −1 , which is completely negligible compared to Γ 0 =0.648·10 −3 cm −1 (note that both Γ δ and Γ 0 scale linearly with pressure, so their ratio is pressure independent).…”

“…It should be emphasized that this conclusion, derived here for the case of the particular purely rotational D 2 lines, in not valid in general. For instance, for fundamental or overtone vibrations of molecular hydrogen the Γ δ contribution (at high pressures) is at the few‐percent level Lorentzian shape of the Dicke‐narrowed profiles Neglecting the above discussed Γ δ , the width of the Dicke‐narrowed line can be expressed as where ω D = ν 0 v m / c (its relation to the Gaussian HWHM is ).…”

“…It should be emphasized that this conclusion, derived here for the case of the particular purely rotational D 2 lines, in not valid in general. For instance, for fundamental or overtone vibrations of molecular hydrogen the Γ δ contribution (at high pressures) is at the few‐percent level …”

Ultrahigh finesse cavity-enhanced spectroscopy for accurate tests of quantum electrodynamics for molecules

“…Furthermore, molecular hydrogen possesses a wide structure of ultra-narrow rovibrational transitions [5] with different sensitivities to the proton charge radius and proton-to-electron mass ratio. Therefore, the recent large progress in both theoretical [1, 2,6] and experimental [7][8][9][10][11] determinations of the rovibrational splitting in different isotopologues of molecular hydrogen makes it a promising system for adjusting several physical constants [12,13]. The most accurate measurements were performed for the HD isotopologue with absolute accuracy claimed to be 20 kHz [14] and 80 kHz [8] for the R(1) 2-0 line.…”

Accurate wavenumber measurements for the S0(0), S0(1), and S0(2) pure rotational Raman lines of D2

“…The main obstacle to obtain accurate experimental data on the H 2 isotopologues is the absence (or in the case of HD, the small magnitude) of a dipole moment, which limits the techniques that can be used to either Raman spectroscopy or ultrasensitive absorption techniques that allow the observation of the extremely weak quadrupole or collision‐induced transitions (weak dipole transitions for HD). The availability of such techniques has prompted, in recent years, the completion of a number of studies on these molecules . Specifically, most of them have used cavity ring‐down spectroscopy or cavity‐enhanced saturated absorption to measure quadrupole and collisionally induced rovibrational transitions in the first and second overtones of H 2 , HD, and D 2 .…”