Theoretical Study Of Properties Of Radium Monofluoride

Heavy diatomic molecules are currently considered to be among the most sensitive systems used in the search for the eEDM and in probing of the Standard Model of particle physics. In certain molecules effects resulting from both parity violation and time-reversal violation (P,T- odd effects) are considerably enhanced with respect to atomic systems. The strength of these interactions grows with atomic number, nuclear spin and nuclear deformation. RaF is of particular interest because it is predicted to have an electronic structure appropriate for laser cooling and also being sensitive to the new phenomena\footnote{L.V. Skripnikov. J. Chem. Phys. 153, 114114, 2020}. The suitability of RaF for laser-cooling depends critically on its energy levels structure, lifetimes of its excited states, vibrational branching ratios and electronic transition probabilities. Although experimental knowledge of radioactive molecules is scarce, a recent work\footnote{R.F. Garcia Ruiz et al. Nature, 581, 396-400, 2020} presented an approach for performing laser spectroscopy of short-lived radioactive molecules, using the highly sensitive collinear resonance ionization method. As an example of the novel technique RaF was used. This work aims to determine properties at the highest possible level of computational accuracy, following the procedure from our earlier work\footnote{Y. Hao et al. J. Chem . Phys. 151, 034302, 2019}, to conclude on the suitability of RaF for laser-cooling and compare with existing experimental data. We present high-accuracy relativistic Fock-Space coupled cluster calculations of the potential energy curves and the spectroscopic constants of the ground state and the lower excited states of RaF. The ionization potential of RaF was calculated and the Franck-Cordon factors were obtained, based on calculated potential energy curves. We have also calculated the TDMs of different transitions using multireference configuration interaction approach. Based on defined TDMs and experimental transitions, lifetimes of the excited states in RaF were determined. The new results are compared with existing theoretical and experimental data

First observation of electric-quadrupole infrared transitions in water vapour

Molecular absorption of infrared radiation is generally due to ro-vibrational electric-dipole transitions. Electric-quadrupole transitions may still occur, but they are typically a million times weaker than electric-dipole transitions, rendering their observation extremely challenging. In polyatomic or polar diatomic molecules, ro-vibrational quadrupole transitions have never been observed. Here, we report the first direct detection of quadrupole transitions in water vapor. The detected quadrupole lines have intensity largely above the standard dipole intensity cut-off of spectroscopic databases and thus are important for accurate atmospheric and astronomical remote sensing

ExoMol molecular line lists XXX: a complete high-accuracy line list for water

A new line list for H$_2$$^{16}$O is presented. This line list, which is called POKAZATEL, includes transitions between rotation-vibrational energy levels up to 41000 cm$^{-1}$ in energy and is the most complete to date. The potential energy surface (PES) used for producing the line list was obtained by fitting a high-quality ab initio PES to experimental energy levels with energies of 41000 cm$^{-1}$ and for rotational excitations up to $J=5$. The final line list comprises all energy levels up to 41000 cm$^{-1}$ and rotational angular momentum $J$ up to 72. An accurate ab initio dipole moment surface (DMS) was used for the calculation of line intensities and reproduces high-precision experimental intensity data with an accuracy close to 1 %. The final line list uses empirical energy levels whenever they are available, to ensure that line positions are reproduced as accurately as possible. The POKAZATEL line list contains over 5 billion transitions and is available from the ExoMol website (www.exomol.com) and the CDS database

Calculated line lists for H216O and H218O with extensive comparisons to theoretical and experimental sources including the HITRAN2016 database

New line lists are presented for the two most abundant water isotopologues; H216O and H218O. The H216O line list extends to 25710 cm with intensity stabilities provided via ratios of calculated intensities obtained from two different semi-empirical potential energy surfaces. The line list for H218O extends to 20000 cm. The minimum intensity considered for all is cm molecule at 296 K, assuming 100% abundance for each isotopologue. Fluctuation of calculated intensities caused by changes in the underlying potential energy are found to be significant, particularly for weak transitions. Direct comparisons are made against eighteen different sources of line intensities, both experimental and theoretical, many of which are used within the HITRAN2016 database. With some exceptions, there is excellent agreement between our line lists and the experimental intensities in HITRAN2016. In the infrared region, many H216O bands which exhibit intensity differences of 5–10% between to the most recent ’POKAZATEL’ line list (Polyansky et al., [Mon. Not. Roy. Astron. Soc. 480, 2597 (2018)] and observation, are now generally predicted to within 1%. For H218O, there are systematic differences in the strongest intensities calculated in this work versus those obtained from semi-empirical calculations. In the visible, computed cross sections show smaller residuals between our work and both HITRAN2016 and HITEMP2010 than POKAZATEL. While our line list accurately reproduces HITEMP2010 cross sections in the observed region, residuals produced from this comparison do however highlight the need to update line positions in the visible spectrum of HITEMP2010. These line lists will be used to update many transition intensities and line positions in the HITRAN2016 database

ExoMol molecular line lists XIX: high-accuracy computed hot line lists for H218O and H217O

Hot line lists for two isotopologues of water, H218O and H217O, are presented. The calculations employ newly constructed potential energy surfaces (PES), which take advantage of a novel method for using the large set of experimental energy levels for H216O to give high-quality predictions for H218O and H217O. This procedure greatly extends the energy range for which a PES can be accurately determined, allowing an accurate prediction of higher lying energy levels than are currently known from direct laboratory measurements. This PES is combined with a high-accuracy, ab initio dipole moment surface of water in the computation of all energy levels, transition frequencies and associated Einstein A coefficients for states with rotational excitation up to J = 50 and energies up to 30 000 cm−1. The resulting HotWat78 line lists complement the well-used BT2 H216O line list. Full line lists are made available online as Supporting Information and at www.exomol.com

Potential energy surface, dipole moment surface and the intensity calculations for the 10 µm, 5 µm and 3 µm bands of ozone

Monitoring ozone concentrations in the Earth's atmosphere using spectroscopic methods is a major activity which undertaken both from the ground and from space. However there are long-running issues of consistency between measurements made at infrared (IR) and ultraviolet (UV) wavelengths. In addition, key O 3 IR bands at 10 µm, 5 µm and 3 µm also yield results which differ by a few percent when used for retrievals. These problems stem from the underlying laboratory measurements of the line intensities. Here we use quantum chemical techniques, first principles electronic structure and variational nuclear-motion calculations, to address this problem. A new high-accuracy ab initio dipole moment surface (DMS) is computed. Several spectroscopically-determined potential energy surfaces (PESs) are constructed by fitting to empirical energy levels in the region below 7000 cm−1 starting from an ab initio PES. Nuclear motion calculations using these new surfaces allow the unambiguous determination of the intensities of 10 µm band transitions, and the computation of the intensities of 10 µm and 5 µm bands within their experimental error. A decrease in intensities within the 3 µm is predicted which appears consistent with atmospheric retrievals. The PES and DMS form a suitable starting point both for the computation of comprehensive ozone line lists and for future calculations of electronic transition intensities

High accuracy water potential energy surface for the calculation of infrared spectra

Transition intensities for small molecules such as water and CO$_2$ can now be computed with such high accuracy that they are being used to systematically replace measurements in standard databases. These calculations use high accuracy ab initio dipole moment surfaces and wavefunctions from spectroscopically-determined potential energy surfaces. Here an extra high accuracy potential energy surface (PES) of the water molecule (\hato) is produced starting from an ab initio PES which is then refined to empirical rovibrational energy levels. Variational nuclear motion calculations using this PES reproduce the fitted energy levels with a standard deviation of 0.011 \cm, approximately three times their stated uncertainty. Use of wavefunctions computed with this refined PES is found to improve the predicted transition intensities for selected (problematic) transitions. A new room temperature line list for H2(16)O is presented. It is suggested that the associated set of line intensities is the most accurate available to date for this species.Comment: 14 pages, 1 figure, 4 table

Room temperature line lists for deuterated water

Line lists are presented for six deuterated isotopologues of water vapor namely HD16O, HD17O, HD18O, D16 2 O, D17 2 O and D18 2 O. These line lists are prepared using empirically-determined energy levels, where available, to provide transition frequencies and high-quality ab initio dipole moment surfaces to provide transition intensities. The reliability of the predicted intensities is tested by computing multiple line lists and analyzing the stability of the results. The resulting intensities are expected to be accurate to a few percent for well-behaved, stable transitions. Complete T = 296 K line lists are provided for each species