Infrared frequency comb spectroscopy of CH2I2: Influence of hot bands and pressure broadening on the ν1 and ν6 fundamental transitions

Chiral molecule candidates for trapped ion spectroscopy by ab initio calculations: From state preparation to parity violation

Parity non-conservation (PNC) due to the weak interaction is predicted to give rise to enantiomer dependent vibrational constants in chiral molecules, but the phenomenon has so far eluded experimental observation. The enhanced sensitivity of molecules to physics beyond the Standard Model (BSM) has led to substantial advances in molecular precision spectroscopy, and these may be applied to PNC searches as well. Specifically, trapped molecular ion experiments leverage the universality of trapping charged particles to optimize the molecular ion species studied toward BSM searches, but in searches for PNC, only a few chiral molecular ion candidates have been proposed so far. Importantly, viable candidates need to be internally cold, and their internal state populations should be detectable with high quantum efficiency. To this end, we focus on molecular ions that can be created by near threshold resonant two-photon ionization and detected via state-selective photo-dissociation. Such candidates need to be stable in both charged and neutral chiral versions to be amenable to these methods. Here, we present a collection of suitable chiral molecular ion candidates we have found, including CHDBrI+ and CHCaBrI+, that fulfill these conditions according to our ab initio calculations. We find that organo-metallic species have low ionization energy as neutrals and relatively high dissociation thresholds. Finally, we compute the magnitude of the PNC values for vibrational transitions for some of these candidates. An experimental demonstration of state preparation and readout for these candidates will be an important milestone toward measuring PNC in chiral molecules for the first time.

Optical frequency comb-based measurements and the revisited assignment of high-resolution spectra of CH2Br2 in the 2960 to 3120 cm-1 region

Brominated organic compounds are toxic ocean-derived trace gases that affect the oxidation capacity of the atmosphere and contribute to its bromine burden. Quantitative spectroscopic detection of these gases is limited by the lack of accurate absorption cross-section data as well as rigorous spectroscopic models. This work presents measurements of high-resolution spectra of dibromomethane, CH₂Br₂, from 2960 cm^-1 to 3120 cm^-1 by two optical frequency comb-based methods, Fourier transform spectroscopy and a spatially dispersive method based on a virtually imaged phased array. The integrated absorption cross-sections measured using the two spectrometers are in excellent agreement with each other within 4%. A revisited rovibrational assignment of the measured spectra is introduced, in which the progressions of features are attributed to hot bands rather than different isotopologues as was previously done. Overall, twelve vibrational transitions, four for each of the three isotopologues CH₂⁸¹Br₂, CH₂⁷⁹Br⁸¹Br, and CH₂⁷⁹Br₂, are assigned. These four vibrational transitions are attributed to the fundamental ν₆ band and the nearby nν₄ + ν₆ - nν₄ hot bands (with n = 1-3) due to the population of the low-lying ν₄ mode of the Br-C-Br bending vibration at room temperature. The new simulations show very good agreement in intensities with the experiment as predicted by the Boltzmann distribution factor. The spectra of the fundamental and the hot bands show progressions of strong Q_Ka(J) rovibrational sub-clusters. The band heads of these sub-clusters are assigned and fitted to the measured spectra, providing accurate band origins and the rotational constants for the twelve states with an average error of 0.0084 cm^-1. A detailed fit of the ν₆ band of the CH₂⁷⁹Br⁸¹Br isotopologue is commenced after assigning 1808 partially resolved rovibrational lines, with the band origin, rotational, and centrifugal constants as fit parameters, resulting in an average error of 0.0011 cm^-1.