Rotational Lines Research Articles

High‐resolution stimulated Raman spectroscopy of low‐frequency rotational transitions: Obtention of collisional broadening coefficients in the rotational S branch of CO perturbed by H2

AbstractWe demonstrate the application of high‐resolution quasi‐continuous (q‐cw) stimulated Raman spectroscopy (SRS) to the study of low‐frequency, pure rotational transitions of molecules in diluted samples in order to obtain collisional information. The main problems encountered in the few pioneering q‐cw SRS rotational works, namely weak signals because of the small population differences between the upper and lower states of the transitions and the presence of alternating current (AC) Stark effect, have been addressed: technical improvements in the optical elements that perform the beam mixing, separation, and filtering have allowed us to use a collinear beam geometry and a triple pass configuration to enhance the Raman signals. The distortions in the line profiles caused by AC Stark effect have been measured and included in the numerical treatment of the spectra. With these extended capabilities, we have been able to register stimulated Raman transitions with wavenumbers as low as ∼ 11.5 cm−1, corresponding to the S(0) pure rotational transition of the molecule of CO. We have applied the setup to the study of collisional broadening of CO rotational lines perturbed by H2 and have obtained broadening coefficients for lines from S(0) to S(20) at 77, 180, and 298 K. A comparison between these anisotropic coefficients and those obtained from IR rovibrational experiments shows excellent agreement. This is, to our knowledge, the first demonstration of the use of rotational SRS for the obtention of collisional information in diluted gas samples.

Shock excitation of H2 in the James Webb Space Telescope era

Context. Molecular hydrogen, H2, is the most abundant molecule in the Universe. Thanks to its widely spaced energy levels, it predominantly lights up in warm gas, T ≳ 102 K, such as shocked regions externally irradiated or not by interstellar UV photons, and it is one of the prime targets of James Webb Space Telescope (JWST) observations. These may include shocks from protostellar outflows, supernova remnants impinging on molecular clouds, all the way up to starburst galaxies and active galactic nuclei. Aims. Sophisticated shock models are able to simulate H2 emission from such shocked regions. We aim to explore H2 excitation using shock models, and to test over which parameter space distinct signatures are produced in H2 emission. Methods. We here present simulated H2 emission using the Paris-Durham shock code over an extensive grid of ~14 000 plane-parallel stationary shock models, a large subset of which are exposed to a semi-isotropic external UV radiation field. The grid samples six input parameters: the preshock density, shock velocity, transverse magnetic field strength, UV radiation field strength, the cosmic-ray-ionization rate, and the abundance of polycyclic aromatic hydrocarbons, PAHs. Physical quantities resulting from our self-consistent calculations, such as temperature, density, and width, have been extracted along with H2 integrated line intensities. These simulations and results are publicly available on the Interstellar Medium Services platform. Results. The strength of the transverse magnetic field, as quantified by the magnetic scaling factor, b, plays a key role in the excitation of H2. At low values of b (≲0.3, J-type shocks), H2 excitation is dominated by vibrationally excited lines; whereas, at higher values (b ≳ 1, C-type shocks), rotational lines dominate the spectrum for shocks with an external radiation field comparable to (or lower than) the solar neighborhood. Shocks with b ≥ 1 can potentially be spatially resolved with JWST for nearby objects. H2 is typically the dominant coolant at lower densities (≲104 cm−3); at higher densities, other molecules such as CO, OH, and H2O take over at velocities ≲20 km s−1 and atoms, for example, H, O, and S, dominate at higher velocities. Together, the velocity and density set the input kinetic energy flux. When this increases, the excitation and integrated intensity of H2 increases similarly. An external UV field mainly serves to increase the excitation, particularly for shocks where the input radiation energy is comparable to the input kinetic energy flux. These results provide an overview of the energetic reprocessing of input kinetic energy flux and the resulting H2 line emission.

Self and N[formula omitted] collisional broadening of far-infrared methane lines at low-temperature with application to Titan

We report the measurement of broadening coefficients of pure rotational lines of methane at different pressure and temperature conditions. A total of 27 far-infrared spectra were recorded at the AILES beamline of the SOLEIL synchrotron at room-temperature, 200K and 120K, in a range of 10 to 800mbar. Self and N2 broadening coefficients and temperature dependence exponents of methane pure rotational lines have been measured in the 73–136cm−1 spectral range using multi-spectrum non-linear least squares fitting of Voigt profiles. These coefficients were used to model spectra of Titan that were compared to a selection of equatorial Cassini/CIRS spectra, showing a good agreement for a stratospheric methane mole fraction of (1.17 ± 0.08)%.

PO+−He collision: ab initio potential energy surface and inelastic rotational rate coefficients

ABSTRACT Computations involving quantum dynamics are performed to attain cross-sections corresponding to rotational de-excitation and excitation rates of the PO+ species including four rotational lines recently detected in the interstellar molecular clouds. New ab initio potential energy surface (PES) for PO+−He collision is constructed by using CCSD(T) method and basis set extrapolated to complete basis set limit (CBS) considering a rigid rotor approximation. The PES is then trained to create neural network (NN) model to construct an augmented surface with angular coordinates at 1° intervals. The PES has a global minimum located at $\theta =110{}^{\circ }$ and R = 3.1 Å. An analytical fitting is performed on the NN surface to obtain the first 41 radial coefficients needed to solve the equations of the coupled-channel method. The essentially precise close coupling approach is used to compute the rotational (de-)excitation cross-sections till 1400 cm−1 with rotational states converged up to 26. Further, these cross-sections are thermally averaged to get the rate coefficients for various rotational transitions till 200 K. The propensity rule favours the odd transitions (Δj = 1) for the current study. The rate for the transition 5 → 4 is found to be higher than transition 1→ 0 by a factor of 3.1 at T = 20 K that decreases to 2.1 at T = 100 K.

Detection of C2H2 using a segmented HC-PCF gas cell

This article demonstrates a fiber laser system that can detect acetylene gas (C2H2) at parts per million (ppmv) levels. The authors investigated the use of off-resonance laser wavelength to develop a highly sensitive detection system. They have developed a gas cell using segmented Hollow-Core Photonic Crystal fiber (HC-PCF), which reduced the filling and evacuation time and thus greatly improved the response time. The gas cell was filled with the gas sample and placed inside the laser cavity, which formed an intracavity laser absorption spectroscopic system. The laser wavelength was selected using a fiber Bragg grating (FBG). The fiber Bragg grating wavelength was centered between the R (5) and R (4) rotational lines of the acetylene ν1 + ν3 combination band, at 1522.22 nm, and used to probe their absorption.

Detection of complex nitrogen-bearing molecule ethyl cyanide towards the hot molecular core G10.47 + 0.03

The studies of the complex organic molecular lines towards the hot molecular cores at millimeter and submillimeter wavelengths provide instructive knowledge about the chemical complexity in the interstellar medium (ISM). We present the detection of the rotational emission lines of the complex nitrogen-bearing molecule ethyl cyanide (C2H5CN) towards the chemically rich hot molecular core G10.47 + 0.03 using the Atacama Large Millimeter/Submillimeter Array (ALMA) band 4 observations. The estimated column density of C2H5CN towards the G10.47 + 0.03 is (7.7 ± 0.5) × $10^{16}\text{ cm}^{-2}$ with the high rotational temperature of 352.9 ± 66.8 K. The estimated fractional abundance of C2H5CN with respect to H2 towards the G10.47 + 0.03 is 5.70 × $10^{-9}$ . We observe that the estimated fractional abundance of C2H5CN is similar to the existing three-phase warm-up chemical modelling abundance of C2H5CN. We also discuss the possible formation mechanism of C2H5CN towards the hot molecular cores, and we claim the barrierless and exothermic radical-radical reaction between CH2 and CH2CN is responsible for the production of low abundance of C2H5CN ( ${\sim} 10^{-9}$ ) in the grain surface of G10.47 + 0.03.

Dissecting the Mid-infrared Heart of M83 with JWST

We present a first look at the MRS observations of the nucleus of the nearby galaxy M83, taken with MIRI on board JWST. The observations show a rich set of emission features from the ionized gas, warm molecular gas, and dust. To begin dissecting the complex processes in this part of the galaxy, we divide the observations into four different regions. We find that the strength of the emission features varies strongly from region to region, with the southeast region displaying the weakest features tracing the dust continuum and interstellar medium (ISM) properties. Comparison between the cold molecular gas traced by the 12CO (1–0) transition with the Atacama Large Millimeter/submillimeter Array and the H2 S(1) transition shows a similar spatial distribution. This is in contrast to the distribution of the much warmer H2 emission from the S(7) transition found to be concentrated around the optical nucleus. We use the rotational emission lines and model the H2 excitation to estimate a total molecular gas mass accounting for the warm H2 component of M(>50 K) = 67.90 (±5.43) × 106 M ⊙. We compare this value to the total gas mass inferred by probing the cold H2 gas through the 12CO (1–0) emission, M(CO) = 17.15 × 106 M ⊙. We estimate that ∼75% of the total molecular gas mass is contained in the warm H2 component. We also identify [O iv] 25.89 μm and [Fe ii] 25.99 μm emission. We propose that the diffuse [Fe ii] 25.99 μm emission might be tracing shocks created during the interactions between the hot wind produced by the starburst and the much cooler ISM above the galactic plane. More detailed studies are needed to confirm such a scenario.

Star Formation and Molecular Gas Diagnostics with Mid- and Far-infrared Emission

With the start of JWST observations, mid-infrared (MIR) emission features from polycyclic aromatic hydrocarbons (PAHs), H2 rotational lines, fine structure lines from ions, and dust continuum will be widely available tracers of gas and star formation rate (SFR) in galaxies at various redshifts. Many of these tracers originate from dust and gas illuminated by UV photons from massive stars, so they generally trace both SFR and gas to varying degrees. We investigate how MIR spectral features from 5–35 μm and photometry from 3.4–250 μm correlate with SFR and molecular gas. In general, we find MIR emission features (i.e., PAHs and H2 rotational lines) trace both CO and SFR better than CO and SFR trace one another. H2 lines and PAH features correlate best with CO. Fine structure lines from ions correlate best with SFR. The [S iii] lines at 18.7 and 33.5 μm, in particular, have a very tight correlation with SFR, and we use them to calibrate new single-parameter MIR tracers of SFR that have negligible metallicity dependence in our sample. The 17 μm/7.7 μm PAH feature ratio increases as a function of CO emission which may be evidence of PAH growth or neutralization in molecular gas. The degree to which dust continuum emission traces SFR or CO varies as a function of wavelength, with continuum between 20 and 70 μm better tracing SFR, while longer wavelengths better trace CO.

Line emission from filaments in molecular clouds

ABSTRACT Filamentary structures are often identified in column density maps of molecular clouds, and appear to be important for both low- and high-mass star formation. Theoretically, these structures are expected to form in regions where the supersonic cloud-scale turbulent velocity field converges. While this model of filament formation successfully reproduces several of their properties derived from column densities, it is unclear whether it can also reproduce their kinematic features. We use a combination of hydrodynamical, chemical, and radiative transfer modelling to predict the emission properties of these dynamically forming filaments in the 13CO, HCN, and N2H+ $J=1{\!-\!}0$ rotational lines. The results are largely in agreement with observations; in particular, line widths are typically subsonic to transonic, even for filaments that have formed from highly supersonic inflows. If the observed filaments are formed dynamically, as our results suggest, no equilibrium analysis is possible, and simulations that presuppose the existence of a filament are likely to produce unrealistic results.

Gas distribution in ODISEA sources from ALMA long-baseline observations in 12CO(2-1)

ABSTRACT The 12CO rotational lines in protoplanetary discs are good tracers of the total spatial extension of the gas component, and potentially planet–disc interactions. We present ALMA long baseline observations of the 12CO(2-1) line of 10 protoplanetary discs from the Ophiuchus DIsc Survey Employing ALMA (ODISEA) project, aiming to set constraints on the gas distribution of these sources. The position angle of the gaseous disc can be inferred for five sources using high-velocity channels, which trace the gas in the inner part of the disc. We compare the high-velocity PAs to the orientations inferred from the continuum, representative of the orientation over ∼53 to 256 au in these resolved discs. We find a significant difference in orientation for DoAr 44, which is evidence of a tilted inner disc. Eight discs show evidence of gas inside inner dust cavities or gaps, and the disc of ISO-Oph 196 is not detected in 12CO(2-1), except for the compact signal located inside its dust cavity. Our observations also point out a possible outflow in WLY 2-63.

Nuclear high-ionisation outflow in the Compton-thick AGN NGC 6552 as seen by the JWST mid-infrared instrument

Context. During the commissioning of the James Webb Space Telescope (JWST), the mid-infrared instrument (MIRI) observed NGC 6552 with the MIRI Imager and the Medium-Resolution Spectrograph (MRS). NGC 6552 is an active galactic nucleus (AGN) at a redshift of 0.0266 (DL = 120 Mpc) classified as a Seyfert 2 nucleus in the optical and Compton-thick AGN in the X-ray. Aims. This work exemplifies and demonstrates the MRS capabilities to study the mid-infrared (mid-IR) spectra and characterise the physical conditions and kinematics of the ionised and molecular gas in the nuclear regions of nearby galaxies. Methods. MIRI Imager observations covers the full NGC 6552 galaxy at 5.6 μm. MRS observations covers its nuclear region (3.6×4.3 kpc at 17.7–27.9 μm) in a wavelength range between 4.9 and 27.9 μm. These observations were obtained with the aim to investigate the persistence of the MIRI detectors (residual signal left from previous bright source observations). However, NGC 6552 observations demonstrate the performance and power of the MIRI instrument even with a non-optimal observational strategy. Results. We obtained the nuclear, circumnuclear, and central mid-IR spectra of NGC 6552. They provide the first clear observational evidence for a nuclear outflow in NGC 6552. The outflow contributes to 67±7% of the total line flux independent of the ionisation potential (27–187 eV) and critical densities (104–4×106 cm−3), showing an average blue-shifted peak velocity of −127±45 km s−1 and an outflow maximal velocity of 698±80 km s−1. Since the mid-IR photons penetrate dusty regions as efficiently as X-ray keV photons, we interpret these results as the evidence for a highly ionised, non-stratified, AGN-powered, and fast outflowing gas in a low density environment (few 103 cm−3) located very close (< 0.2 kpc) to the Compton-thick AGN. Nine pure rotational molecular Hydrogen lines are detected and spectrally resolved, and exhibit symmetric Gaussian profiles, consistent with the galactic rotation, and with no evidence of outflowing H2 material. We detect a warm H2 mass of 1.9 ± 1.1 × 107 M⊙ in the central region (1.8 kpc in diameter) of the galaxy, with almost 30% of that mass in the circumnuclear region. Line ratios confirm that NGC 6552 has a Seyfert nucleus with a black hole mass estimated in the range of 0.6–6 million solar masses. Conclusions. This work demonstrates the power of the newly commissioned MIRI Medium Resolution Spectrograph to reveal new insights in the kinematics and ionisation state of the interstellar medium around the dusty nuclear regions of nearby active galaxies.

A Broadband Circularly Polarized Single-Layer Metasurface Antenna Using Characteristic-Mode Analysis

In this work, we propose a low-profile single-layer coplanar waveguide (CPW)-fed metasurface (MTS) antenna with broadband circular polarization (CP) radiation. With the help of characteristic-mode analysis (CMA), a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textbf {3}\times \textbf {4}$ </tex-math></inline-formula> MTS is analyzed to reveal the useful modes supported by the structure. Consequently, two modes with orthogonal current distribution, broadside radiation, and nearly <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm{90}^{\circ} $ </tex-math></inline-formula> phase difference over a wide frequency band are chosen as operation modes. Moreover, the modal near field of the aforementioned modes shows that, unlike conventional microstrip patches, the entire proposed MTS supports two kinds of extraordinary TM modes, namely, e-TM30 and e-TM04. Accordingly, a rotated CPW feeding line is used to excite the two modes without adding an extra layer as reported in the literature, making the design simpler and easier to manufacture. Based on that, a low profile antenna of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textbf {0.058}\lambda _{0}$ </tex-math></inline-formula> has been designed and fabricated. The measured results show an impedance bandwidth (IBW) of 25% (4.870–6.26 GHz), 3 dB axial ratio (AR) band of 19.42% (5.30–6.44 GHz), and a maximum gain of 8 dBi.

Astrophysical properties of 15062 Gaia DR3 gravity-mode pulsators

Context. Gravito-inertial asteroseismology came into existence thanks to high-precision CoRoT and Kepler space photometric light curves. So far, it has given rise to the internal rotation frequency of a few hundred intermediate-mass stars, yet only several tens of these have been weighed, sized, and age-dated with high precision using asteroseismic modelling. Aims. We aim to increase the sample of optimal targets for future gravito-inertial asteroseismology by assessing the properties of 15062 newly found Gaia DR3 gravity-mode pulsators. We also wish to investigate whether or not there is a connection between their fundamental parameters, the dominant mode, and their spectral line broadening as measured by Gaia. Methods. After reclassifying about 22% of the F-type gravity-mode pulsators as B-type according to their effective temperature, we constructed histograms of the fundamental parameters and mode properties of the 15062 new Gaia DR3 pulsators. We compared these histograms with those of 63 Kepler bona fide class members. We fit errors-in-variables regression models to couple the effective temperature, luminosity, gravity, and oscillation properties to the two Gaia DR3 parameters capturing spectral line broadening for a fraction of the pulsators. Results. We find that the selected 15062 gravity-mode pulsators have properties that are fully in line with those of their well-known Kepler analogues, revealing that Gaia has a role to play in asteroseismology. The dominant ɡ-mode frequency is a significant predictor of the spectral line broadening for the class members for which this quantity has been measured. We show that the Gaia vbroad parameter captures the joint effect of time-independent intrinsic and rotational line broadening and time-dependent tangential pulsational broadening. Conclusions. While the Gaia mission was not designed to detect non-radial oscillation modes, its multitude of data and homogeneous data treatment allow us to identify a vast number of new gravity-mode pulsators that have fundamental parameters and dominant mode properties in agreement with those of such Kepler bona fide pulsators. This large new sample of Gaia DR3 pulsators can be followed up with dedicated high-precision photometric or high-resolution spectroscopic instruments to embark on asteroseismic modelling.

Crystallization features of YBa2Cu3O7-δ single crystals in 2YBa4Cu3O9-δ + BaCu2O2 + CuO2 system

In this article, a consistent study of phase transformations during the crystallization of YBa2Cu3O7-δ compound was carried out using XRD, thermogravimetric and differential thermal analyzes, as well as optical microscopy. When studying the microstructure and elemental composition in the reaction zone in the process of obtaining single crystals by the crucible-less method, the products of chemical reactions were identified depending on the composition of the reacting components and synthesis conditions. It has been established that the use of precursors Y2BaCuO5, YBa4Cu3O9-δ and ВаCu2O2 as initial reagents has made it possible to carry out the direct synthesis of YBa2Cu3O7-δ single crystals without the formation of intermediate phases. The superconductor has been synthesized at 1270 K on single-crystal MgO substrates with the (001) orientation, since their surface is poorly wetted by the melt solution and stimulates the YBa2Cu3O7-δ nucleation process. This ensures the minimum loss of the liquid fraction formed in the sample. The growth conditions for YBa2Cu3O7-δ single crystals have been studied and optimized. It has been experimentally revealed that the use of combined cooling conditions leads to an increase in the size of single crystals and a reduction in the time of their growth without changing the quality and crystal structure. The investigation showed that the largest volume (50 mm3) was achieved for single-phase YBa2Cu3O7-δ single crystals grown at a cooling rate of 0.5 deg/h in the temperature range 1260–1240 K and at a rate of 1.2 deg/h in the range 1240–1210 K. An analysis of the Laue rotation lines obtained in this work indicates the presence of blocks in single crystals cooled in the temperature range 1243–1193 K at a cooling rate of 1.5 deg/h and their absence in crystals cooled at 1.2 deg/h. An assessment of the degree of perfection of the structure by the width of the rocking curves at half-height of the X-ray reflection (006) showed that the width of the rocking curves of 0.36 deg indicates the absence of structural defects, such as twins, blockiness, and shear defects.

OH mid-infrared emission as a diagnostic of H2O UV photodissociation

Context. Water photodissociation in the 114–143 nm UV range forms excited OH which emits at mid-infrared (MIR) wavelengths via highly excited rotational lines. These lines have only been detected with Spitzer in proto-planetary disks and shocks. Previous studies have shown that they are a unique diagnostic for water photodissociation. Thanks to its high sensitivity and angular resolution, the James Webb Space Telescope (JWST) could be able to detect them in other environments such as interstellar photodissociation regions (PDRs). Aims. Our goal is to predict OH MIR lines for a large range of thermal pressures and UV fields in PDRs. Methods. We use the Meudon PDR Code to compute the thermal and chemical structure of PDRs. In order to predict the emerging spectrum of OH, we amended the code to include prompt emission induced by H2O photodissociation between 114 and 143 nm. We performed a detailed study of the influence of thermal pressure (Pth/k = nHTK) and UV field strength on the integrated intensities and their detectability with the JWST. Results. OH MIR emission is predicted to originate very close to the H0/H2 transition and is directly proportional to the column density of water photodissociated in that layer. Because gas-phase neutral-neutral reactions forming water require relatively high temperatures (TK ≳ 300 K), the resulting OH MIR lines are primarily correlated with the temperature at this position, and are therefore brighter in regions with high pressure. This implies that these lines are predicted to be only detectable in strongly irradiated PDRs (G0incident &gt; 103) with high thermal pressure (Pth/k ≳ 5x107 K cm–3). In the latter case, OH MIR lines are less dependent on the strength of the incident UV field. The detection of such lines in PDRs such as the Orion bar – which should be possible – is also investigated and we show that the line-to-continuum ratio could be a major limitation for detection because of instrumental limitations. Conclusions. OH MIR lines observable by JWST are a promising diagnostic for dense and strongly irradiated PDRs and proplyds. Their intensities are directly proportional to the amount of water photodissociated and they are therefore an indirect but sensitive probe of the gas temperature at the H0/H2 transition.

High-resolution vibrational predissociation spectroscopy of I− · H2O by single-mode CW infrared excitation in a 3D cryogenic ion trap

We describe the integration of a tunable, single-mode, continuous wave infrared laser into a cryogenic ion spectroscopy experiment to measure the rovibrational spectrum of the complex in the OH stretching region. These upper levels lie about 300 cm−1 above the dissociation threshold. The measurements are carried out by loading the ions in a radiofrequency ion trap at 10 Hz and cooling them to 5 K with pulsed He buffer gas. IR photodissociation (PD) of the complex is monitored by recording the product yield by time-of-flight mass spectrometry as a function of laser wavelength. Very narrow ( v∼75 MHz) rotational lines are observed throughout the spectrum, indicating long (ca. 2 ns) lifetimes for the excited metastable rovibrational levels. Rotational analysis of the band arising from the K” = 1 to K’ = 2 transition of the free OH stretching fundamental yields the structure of the complex for the first time. Over 50% of the trapped ion ensemble in the trap can be photodissociated upon excitation of a single rotational line. This enables very high signal-to-noise in the PD spectrum, and is traced to a mechanism in which the ground state rotational levels are rapidly equilibrated by collisions with the buffer gas.

Improving the upper atmospheric temperature accuracy of the ground-based instrument by eliminating noise ways.

In view of the special properties of the upper atmosphere at the altitude of 80-120km, a ground-based passive remote sensing instrument ground-based airglow volume emission rate and temperature imaging interferometer (GBAVTII) is built to detect the atmospheric temperature used O 2(0-1) spectral line of night airglow at the altitude of 94km. In the process of photographing the upper atmosphere airglow with the GBAVTII, the stray light (white noise) such as moonlight, city lights, and starlight will be affected. In this paper, the theoretical expression of denoising is derived based on the rotational line temperature measurement of diatomic O 2(0-1) airglow. Through a slight adjustment of different parameters in the forward equation of the GBAVTII and noise reduction in laboratory flat-field fine calibration, and other denoising methods in the GBAVTII image processing process, the maximum accuracy of the GBAVTII detection of the upper atmospheric temperature is enhanced to 2.4K. Also, the minimum error of the GBAVTII detecting data with the satellite instrument sounding of atmosphere using broadband emission radiometry is 0.4K. Thus, the absolute accuracy of the GBAVTII in detecting the upper atmospheric temperature can be improved to ±(0.4-2.4)K through the theory and method studied in this paper.

Structure and nuclear quadrupole coupling interaction in hydroxylamines: The rotational spectrum of N,N-diethyl(2H)hydroxylamine

The ground-state rotational spectrum of N,N-diethyl(2H)hydroxylamine (C2H5-NOD-C2H5) was measured by Fourier transform microwave spectroscopy. Six rotational transition lines were assigned to the most stable conformer with the alkyl chain in the trans arrangement and the hydroxyl trans to the bisector of the CNC angle, that is, with the NOD frame in the bc-symmetry plane. Rotational constants are A= 7210.938(2), B= 2018.628(1), and C= 1739.696(1) MHz. These data together with those previously determined for the parent species and 13C and 15N isotopologues, were used to determine a partial r0 structure. The hyperfine structure due to the nuclear quadrupole coupling (NQC) interaction of both 14N and D nuclei was disentangled allowing to obtain the diagonal NQC-constants. On the basis of the determined geometry, the NQC-tensor values in the electric field-gradient principal axis system were determined (χxxN= 0.71, χyyN= 5.90, χzzN= −6.61 MHz; χxxD= −0.11, χyyD= −0.15, χzzD= 0.26 MHz). Comparison with other amines shows that using ammonia as reference, χzzN can be estimated with an additive model: +0.4 and +1.7 MHz from hydrogen to alkyl and hydroxyl substitution, respectively. From the analysis of the available data on the 1:1 water complex of N,N-diethylhydroxylamine, a 8% electric field gradient decrease at the nitrogen nucleus due to the formation of the hydrogen bond involving the nitrogen lone pair was found.

PHANGS–JWST First Results: A Global and Moderately Resolved View of Mid-infrared and CO Line Emission from Galaxies at the Start of the JWST Era

We explore the relationship between mid-infrared (mid-IR) and CO rotational line emission from massive star-forming galaxies, which is one of the tightest scalings in the local universe. We assemble a large set of unresolved and moderately (∼1 kpc) spatially resolved measurements of CO (1–0) and CO (2–1) intensity, I CO, and mid-IR intensity, I MIR, at 8, 12, 22, and 24 μm. The I CO versus I MIR relationship is reasonably described by a power law with slopes 0.7–1.2 and normalization I CO ∼ 1 K km s−1 at I MIR ∼ 1 MJy sr−1. Both the slopes and intercepts vary systematically with choice of line and band. The comparison between the relations measured for CO (1–0) and CO (2–1) allow us to infer that , in good agreement with other work. The 8 μm and 12 μm bands, with strong polycyclic aromatic hydrocarbon (PAH) features, show steeper CO versus mid-IR slopes than the 22 and 24 μm, consistent with PAH emission arising not just from CO-bright gas but also from atomic or CO-dark gas. The CO-to-mid-IR ratio correlates with global galaxy stellar mass (M ⋆) and anticorrelates with star formation rate/M ⋆. At ∼1 kpc resolution, the first four PHANGS–JWST targets show CO-to-mid-IR relationships that are quantitatively similar to our larger literature sample, including showing the steep CO-to-mid-IR slopes for the JWST PAH-tracing bands, although we caution that these initial data have a small sample size and span a limited range of intensities.

Measurement of self-broadening coefficients and line intensities of ν1 + ν3 + ν4 ‒ ν4 band of acetylene in 1.5 μm spectral region: External cavity diode laser based absorption study

Acetylene is considered to be an important molecule for spectroscopic research due to its role in environmental chemistry, astrophysics, biochemistry and photochemistry of various planets. The high resolution spectroscopic studies of acetylene (12C2H2) in the 6474–6515 cm−1 spectral range have been performed using in-house developed external-cavity diode laser absorption spectroscopy technique. The study is focused on experimental measurement of self-broadening coefficients (γself) and line intensities of 27 l-doublet ro-vibrational lines belonging to the P-branch transition of ν1 + ν3 + ν4 ‒ ν4 hot band lying in the 6474–6515 cm−1 spectral range. The γself and line intensity have been retrieved by modelling of each experimentally observed rotational line with standard Voigt line profile using custom written python based computer program. The measured γself and line intensities were compared with the values present in HITRAN2020 database, showing mean difference of about -1.9% and 2.48%, respectively. In contrast to the line intensity, where rotational and symmetry dependency are readily visible, γself exhibits only rotational dependency. The l-type doubling constants of both ν1 + ν3 + ν4 and ν4 states of ν1 + ν3 + ν4 ‒ ν4 hot band have also been obtained. Detailed understanding of these molecular parameters will play an important role in modelling of planetary atmospheres.