Lamb-dip cavity ring-down spectroscopy of acetylene at 1.4 μm

Doppler-free saturated-absorption Lamb dips are observed for weak vibration-rotation transitions of C2H2 between 7167 and 7217 cm−1, using a frequencycomb assisted cavity ring-down spectrometer based on the use of a pair of phase-locked diode lasers. We measured the absolute center frequency of sixteen lines belonging to the 2ν3 + ν15 band, targeting ortho and para states of the molecule. Line pairs of the P and Q branches were selected so as to form a “V”-scheme, sharing the lower energy level. Such a choice made it possible to determine the rotational energy separations of the excited vibrational state for J-values from 11 to 20. Line-center frequencies are determined with an overall uncertainty between 2 and 13 kHz. This is over three order of magnitude more accurate than previous experimental studies in the spectral region around the wavelength of 1.4 μm. The retrieved energy separations provide a stringent test of the so-called MARVEL method recently applied to acetylene.

Locomotion of Self-Excited Vibrating and Rotating Objects in Granular Environments

Many reptiles, known as ‘sand swimmers’, adapt to their specific environments by vibrating or rotating their body. To understand these type of interactions of active objects with granular media, we study a simplified model of a self-excited spherical object (SO) immersed in the granular bed, using three-dimensional discrete element method (DEM) simulations. Modelling the vibration by an oscillatory motion, we simulate the longitudinal locomotion of the SO in three modes: transverse vibration, rotation around different axes, and a combination of both. We find that the mode of oscillation in y direction coupled with rotation around x-axis is optimal in the sense that the SO rises fastest, with periodic oscillations, in the z direction while remaining stable at the initial x position. We analyze the physical mechanisms governing the meandering up or down and show that the large oscillations are caused by an asynchronous changes between the directions of oscillation and rotation. We also observed that the SO’s rising rate is sensitive to three parameters: the oscillation amplitude, the oscillation frequency, f, and the rotation angular velocity, Ω. We report the following results. 1. When the frequencies of the rotation and transverse motion are synchronised, SO rises when Ω<0 and sinks when Ω>0; the average rising/sinking rate is proportional to |Ω|. 2. The rising rate increases linearly with the oscillation amplitude. 3. There exists a critical oscillation frequency, above and below which the rising mechanisms are different. Our study reveals the range of parameters that idealized ‘swimmers’ need to use to optimize performance in granular environments.

Уширение и сдвиг линий основной колебательно-вращательной полосы молекул фтористого водорода молекулами SF-=SUB=-6-=/SUB=- и H-=SUB=-2-=/SUB=-

Foreign gas broadening and shift of the vibration-rotation lines in the fundamental band of hydrogen fluoride have been investigated. Using mathematical modeling of measuring the absorption of radiation of an electric discharge HF laser, the possibility of correct calculations of both broadening and shift of HF lines by foreign gases were determined. Measurements for two foreign gases (Ar and N2 for which there are literature data) were made in order to test this approach. The obtained results have been well matched with existing literature data. After that, measurements were carried out on two transitions P(7) and P(8) for SF6 (for which neither broadening nor the shift are known) and for H2 (only broadening is known for overtone band). The obtained results were compared with scarce literature data.

Анализ спектра высокого разрешения молекул в дублетных электронных состояниях: фундаментальная полоса ν-=SUB=-3-=/SUB=- диоксида хлора (-=SUP=-16-=/SUP=-O-=SUP=-35-=/SUP=-Cl-=SUP=-16-=/SUP=-O) в основном электронном состоянии X-=SUP=-2-=/SUP=-B-=SUB=-1-=/SUB=-

Vibration-rotation structure of the ν3 band of ClO2 was recorded with a Bruker IFS 125 HR Fourier spectrometer with a resolution of 0.0015 cm–1. Ro-vibrational analysis of the recorded experimental spectrum was made with an improved effective Hamiltonian and developed computer code for ro–vibrational spectra of open–shell free radical molecules including spin–rotation interactions. About 4200 transitions with the maximum values Nmax = 68 and Kamax = 21 belonging to the ν3 band were assigned and subsequently used to determine a set of 13 spectroscopic parameters of the vibrational state under study. The root-mean-square deviation of the results is drms = 2.4 ∙ 10-4 cm-1.

Constraining nucleosynthesis in two CEMP progenitors using fluorine

ABSTRACT We present new fluorine abundance estimations in two carbon enhanced metal-poor (CEMP) stars, HE 1429−0551 and HE 1305+0007. HE 1429−0551 is also enriched in slow neutron-capture process (s-process) elements, a CEMP-s, and HE 1305+0007 is enhanced in both, slow and rapid neutron-capture process elements, a CEMP-s/r. The F abundances estimates are derived from the vibration–rotation transition of the HF molecule at 23358.6 Å using high-resolution infrared spectra obtained with the Immersion Grating Infrared Spectrometer (IGRINS) at the 4-m class Lowell Discovery Telescope. Our results include an F abundance measurement in HE 1429−0551 of A(F) = +3.93 ([F/Fe] = +1.90) at [Fe/H] = −2.53, and an F upper limit in HE 1305+0007 of A(F) &lt; +3.28 ([F/Fe] &lt; +1.00) at [Fe/H] = −2.28. Our new derived F abundance in HE 1429−0551 makes this object the most metal-poor star where F has been detected. We carefully compare these results with literature values and state-of-the-art CEMP-s model predictions including detailed asymptotic giant branch (AGB) nucleosynthesis and binary evolution. The modelled fluorine abundance for HE 1429−0551 is within reasonable agreement with our observed abundance, although is slightly higher than our observed value. For HE 1429−0551, our findings support the scenario via mass transfer by a primary companion during its thermally pulsing phase. Our estimated upper limit in HE 1305+0007, along with data from the literature, shows large discrepancies compared with AGB models. The discrepancy is principally due to the simultaneous s- and r-process element enhancements which the model struggles to reproduce.

Far-infrared laboratory spectroscopy of aminoacetonitrile and first interstellar detection of its vibrationally excited transitions

Context. Aminoacetonitrile, a molecule detected in the interstellar medium only toward the star-forming region Sagittarius B2 (Sgr B2), is considered an important prebiotic species; in particular, it is a possible precursor of the simplest amino acid glycine. To date, observations have been limited to ground state emission lines, whereas transitions from within vibrationally excited states remained undetected. Aims. We wanted to accurately determine the energies of the low-lying vibrational states of aminoacetonitrile, which are expected to be populated in Sgr B2(N1), the main hot core of Sgr B2(N). This step is fundamental in order to properly evaluate the vibration-rotation partition function of aminoacetonitrile as well as the line strengths of the rotational transitions of its vibrationally excited states. This is necessary to derive accurate column densities and secure the identification of these transitions in astronomical spectra. Methods. The far-infrared ro-vibrational spectrum of aminoacetonitrile has been recorded in absorption against a synchrotron source of continuum emission. Three bands, corresponding to the lowest vibrational modes of aminoacetonitrile, were observed in the frequency region below 500 cm−1. The combined analysis of ro-vibrational and pure rotational data allowed us to prepare new spectral line catalogs for all the states under investigation. We used the imaging spectral line survey ReMoCA performed with ALMA to search for vibrationally excited aminoacetonitrile toward Sgr B2(N1). The astronomical spectra were analyzed under the local thermodynamic equilibrium (LTE) approximation. Results. Almost 11 000 lines have been assigned during the analysis of the laboratory spectrum of aminoacetonitrile, thanks to which the vibrational energies of the v11 = 1, v18 = 1, and v17 = 1 states have been determined. The whole dataset, which includes high J and Ka transitions, is well reproduced within the experimental accuracy. Reliable spectral predictions of pure rotational lines can now be produced up to the THz region. On the basis of these spectroscopic predictions, we report the interstellar detection of aminoacetonitrile in its v11 = 1 and v18 = 1 vibrational states toward Sgr B2(N1) in addition to emission from its vibrational ground state. The intensities of the identified v11 = 1 and v18 = 1 lines are consistent with the detected v = 0 lines under LTE at a temperature of 200 K for an aminoacetonitrile column density of 1.1 × 1017 cm−2. Conclusions. This work shows the strong interplay between laboratory spectroscopy exploiting (sub)millimeter and synchrotron-based far-infrared techniques, and observational spectral surveys to detect complex organic molecules in space and quantify their abundances.

First detection of ozone in the mid-infrared at Mars: implications for methane detection

Aims. The ExoMars Trace Gas Orbiter was sent to Mars in March 2016 to search for trace gases diagnostic of active geological or biogenic processes. Methods. We report the first observation of the spectral features of Martian ozone (O3) in the mid-infrared range using the Atmospheric Chemistry Suite Mid-InfaRed (MIR) channel, a cross-dispersion spectrometer operating in solar occultation mode with the finest spectral resolution of any remote sensing mission to Mars. Results. Observations of ozone were made at high northern latitudes (>65°N) prior to the onset of the 2018 global dust storm (Ls = 163–193°). During this fast transition phase between summer and winter ozone distribution, the O3 volume mixing ratio observed is 100–200 ppbv near 20 km. These amounts are consistent with past observations made at the edge of the southern polar vortex in the ultraviolet range. The observed spectral signature of ozone at 3000–3060 cm−1 directly overlaps with the spectral range of the methane (CH4) ν3 vibration-rotation band, and it, along with a newly discovered CO2 band in the same region, may interfere with measurements of methane abundance.