5,025 research outputs found
Methanol as a tracer of fundamental constants
The methanol molecule CH3OH has a complex microwave spectrum with a large
number of very strong lines. This spectrum includes purely rotational
transitions as well as transitions with contributions of the internal degree of
freedom associated with the hindered rotation of the OH group. The latter takes
place due to the tunneling of hydrogen through the potential barriers between
three equivalent potential minima. Such transitions are highly sensitive to
changes in the electron-to-proton mass ratio, mu = m_e/m_p, and have different
responses to mu-variations. The highest sensitivity is found for the mixed
rotation-tunneling transitions at low frequencies. Observing methanol lines
provides more stringent limits on the hypothetical variation of mu than ammonia
observation with the same velocity resolution. We show that the best quality
radio astronomical data on methanol maser lines constrain the variability of mu
in the Milky Way at the level of |Delta mu/mu| < 28x10^{-9} (1sigma) which is
in line with the previously obtained ammonia result, |Delta mu/mu| < 29x10^{-9}
(1\sigma). This estimate can be further improved if the rest frequencies of the
CH3OH microwave lines will be measured more accurately.Comment: 7 pages, 1 table, 1 figure. Accepted for publication in Ap
Sensitivity of the H3O+ inversion-rotational spectrum to changes in m_e/m_p
Quantum mechanical tunneling inversion transition in ammonia NH3 is actively
used as a sensitive tool to study possible variations of the electron-to-proton
mass ratio, mu = m_e/m_p. The molecule H3O+ has the inversion barrier
significantly lower than that of NH3. Consequently, its tunneling transition
occurs in the far-infrared (FIR) region and mixes with rotational transitions.
Several such FIR and submillimiter transitions are observed from the
interstellar medium in the Milky Way and in nearby galaxies. We show that the
rest-frame frequencies of these transitions are very sensitive to the variation
of mu, and that their sensitivity coefficients have different signs. Thus, H3O+
can be used as an independent target to test hypothetical changes in mu
measured at different ambient conditions of high (terrestrial) and low
(interstellar medium) matter densities. The environmental dependence of mu and
coupling constants is suggested in a class of chameleon-type scalar field
models - candidates to dark energy carrier.Comment: 8 pages, 2 figures, accepted to ApJ; v2: reformatted for ApJ and
discussion of systematics significantly extende
Study of quadrupole polarizabilities with combined configuration interaction and coupled-cluster method
The recently developed method combining the configuration interaction and the
coupled-cluster method was demonstrated to provide accurate treatment of
correlation corrections in divalent atomic systems [M.S.Safronova, M.G.Kozlov,
and C.W.Clark, Phys. Rev. Lett. 107, 143006 (2011)]. We have extended this
approach to the calculation of quadrupole polarizabilities alpha_2 and applied
it to evaluate alpha_2 for the ground state of Mg and Mg-like Si^{2+}.
Performing the calculations in three different approximations of increasing
accuracy allowed us to place the upper bounds on the uncertainty of the final
results. The recommended values alpha_2(3s^2 1S0)= 35.86(13) a.u. for Si^{2+}
and alpha_2(3s^2 1S0)= 814(3) a.u. for Mg are estimated to be accurate to
0.37%. Differences in quadrupole polarizability contributions in neutral Mg and
Si^{2+} ion are discussed.Comment: 6 pages, submitted to Phys. Rev.
Calculation of hyperfine structure constants for ytterbium
We calculate energies and hyperfine structure constants A and B for low-lying
levels of Yb. The latter is treated as a two-electron atom. To account
for valence-valence correlations the configuration interaction method is used.
Valence-core correlations are accounted for within the many-body perturbation
theory which is used to construct effective two-electron operators in the
valence space.Comment: 8 pages, latex, iopart class or ioplppt style, submitted to J. Phys.
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