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

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

The W2020 Database of Validated Rovibrational Experimental Transitions and Empirical Energy Levels of Water Isotopologues. II. H₂¹⁷O and H₂¹⁸O with an Update to H₂¹⁶O

The W2020 database of validated experimental transitions and accurate empirical energy levels of water isotopologues, introduced in the work of Furtenbacher et al. [J. Phys. Chem. Ref. Data 49, 033101 (2020)], is updated for H216O and newly populated with data for H217O and H218O. The H217O/H218O spectroscopic data utilized in this study are collected from 65/87 sources, with the sources arranged into 76/99 segments, and the data in these segments yield 27 045/66 166 (mostly measured) rovibrational transitions and 5278/6865 empirical energy levels with appropriate uncertainties. Treatment and validation of the collated transitions of H216O, H217O, and H218O utilized the latest, XML-based version of the MARVEL (Measured Active Rotational-Vibrational Energy Levels) protocol and code, called xMARVEL. The empirical rovibrational energy levels of H217O and H218O form a complete set through 3204 cm-1 and 4031 cm-1, respectively. Vibrational band origins are reported for 37 and 52 states of H217O and H218O, respectively. The spectroscopic data of this study extend and improve the data collated by an International Union of Pure and Applied Chemistry Task Group in 2010 [J. Tennyson et al., J. Quant. Spectrosc. Radiat. Transfer 110, 2160 (2010)] as well as those reported in the HITRAN2016 information system. Following a minor but significant update to the W2020-H216O dataset, the joint analysis of the rovibrational levels for the series H216O, H217O, and H218O facilitated development of a consistent set of labels among these three water isotopologues and the provision of accurate predictions of yet to be observed energy levels for the minor isotopologues using the combination of xMARVEL results and accurate variational nuclear-motion calculations. To this end, 9925/8409 pseudo-experimental levels have been derived for H217O/H218O, significantly improving the coverage of accurate lines for these two minor water isotopologues up to the visible region. The W2020 database now contains almost all of the transitions, apart from those of HD16O, required for a successful spectroscopic modeling of atmospheric water vapor

Analysis of the Red and Green Optical Absorption Spectrum of Gas Phase Ammonia

Room temperature NH3 absorption spectra recorded at the Kitt Peak National Solar Observatory in 1980 are analyzed. The spectra cover two regions in the visible: 15,200 - 15,700 cm-1 and 17,950 - 18,250 cm-1. These high overtone rotation-vibration spectra are analyzed using both combination differences and variational line lists. Two variational line lists were computed using the TROVE nuclear motion program: one is based on an ab initio potential energy surface (PES) while the other used a semi-empirical PES. Ab initio dipole moment surfaces are used in both cases. 95 energy levels with J = 1 - 7 are determined from analysis of the experimental spectrum in the 5vNH (red) region and 46 for 6vNH (green) region. These levels span four vibrational bands in each of the two regions, associated with stretching overtones

Measurement and calculation of CO (7-0) overtone line intensities

Intensities of 14 lines in the sixth overtone (7-0) band of carbon monoxide (12C16O) are measured in the visible range between 14 300 and 14 500 cm-1 using a frequency-stabilized cavity ring-down spectrometer. This is the first observation of such a high and weak overtone spectrum of the CO molecule. A theoretical model is constructed and tested based on the use of a high accuracy ab initio dipole moment curve and a semi-empirical potential energy curve. Accurate studies of high overtone transitions provide a challenge to both experiment and theory as the lines are very weak: below 2 × 10-29 cm molecule-1 at 296 K. Agreement between theory and experiment within the experimental uncertainty of a few percent is obtained. However, this agreement is only achieved after issues with the stability of the Davidson correction to the multi-reference configuration interaction calculations are addressed