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Astronomical precision spectroscopy underpins searches for life beyond Earth, direct observation of the expanding Universe and constraining the potential variability of physical constants on cosmological scales. Laser frequency combs can provide the required accurate and precise calibration to the astronomical spectrographs. For cosmological studies, extending the calibration with such astrocombs to the ultraviolet spectral range is desirable, however, strong material dispersion and large spectral separation from the established infrared laser oscillators have made this challenging. Here, we demonstrate astronomical spectrograph calibration with an astrocomb in the ultraviolet spectral range below 400 nm. This is accomplished via chip-integrated highly nonlinear photonics in periodically-poled, nano-fabricated lithium niobate waveguides in conjunction with a robust infrared electro-optic comb generator, as well as a chip-integrated microresonator comb. These results demonstrate a viable route towards astronomical precision spectroscopy in the ultraviolet and could contribute to unlock the full potential of next-generation ground-based and future space-based instruments. Here the authors demonstrate ultraviolet astronomical frequency combs, derived from the near-infrared domain via efficient harmonic generation in nanophotonic waveguides, to provide precision calibration to astronomical spectrographs for exoplanet science and precision cosmology. [ABSTRACT FROM AUTHOR]

Claudio Mendoza (1951-2024) was a renowned computational physicist known for his humor, irreverence, and intellectual activity. He was born in Venezuela and grew up in a small village where his family, along with other artists and intellectuals, created an environment of intense intellectual activity. Claudio pursued his education in London and later returned to Venezuela to work as a faculty member before completing his Ph.D. at University College London. He made significant contributions to projects on atomic data for astrophysical applications and X-ray spectroscopy. Claudio faced challenges in his career due to his public opinions, leading to his retirement and emigration to the United States. He passed away in 2024 after battling lung cancer. [Extracted from the article]

The main isotopologue of 2-hydroxyacetonitrile (glycolonitrile; HOCH2CN) has recently been detected in the interstellar medium (ISM). To date, no rotational spectroscopy of 2-hydroxyacetonitrile 13C-isotopologues studies has been carried out and only few centimetre-wave measurements of one deuterated isotopologue (DOCH2CN) exist. The rotational spectrum of the 2-hydroxyacetonitrile 13C-isotopologues and DOCH2CN was investigated from 150 to 530 GHz. As the parent isotopic species, the other 2-hydroxyacetonitrile isotopologues exhibit large amplitude motion due to the torsion of the hydroxyl group. The analyses of the spectra were carried out using the reduced axis system (RAS) formalism and Watson's S-reduction Hamiltonian implemented in the spfit code. More than 3000 lines were fitted for the three studied isotopologues, with quantum number values reaching 60–67 for J and 21–25 for K a depending on the species. Accurate line lists up to 600 GHz and partition functions are provided. A search for these isotopologues in SMM1-a and IRAS 16293 B surveys resulted in non-detections; upper limits to the column density were determined. The accurate spectroscopic prediction of their spectra provided in this work will allow astronomers to continue the search for 2-hydroxyacetonitrile isotopologues in the ISM. [ABSTRACT FROM AUTHOR]

We used two different methods of statistical analysis—cluster analysis and principal component analysis—to analyze the concentrations of principal chemical components (Si, Mg, Ca, Fe, Ni) and Co in ordinary chondrites. The analysis is based predominantly on published data (metadata). In total, chemical composition data from 646 ordinary chondrites were used in the statistical analysis. The aim of this analysis was to establish whether it would be possible or not to distinguish H, L, and LL chondrites based on the concentrations of major elements and Co in their bulk chemical compositions. It was also important to determine what conclusions such an analysis could enable to draw about matter differentiation in the formation environments of primordial parent bodies of particular ordinary chondrite groups (H, L, and LL). Another aim of the statistical analysis was to determine whether the distribution of Fe and Ni (with Co admixtures) is independent of petrographic types within particular groups of chondrites. This is of crucial importance for determining the distribution of FeNi(Co) ore occurrences in potential extraterrestrial deposits on modern asteroids—the sources of ordinary chondrites. The obtained results of statistical analyses confirmed that a clear‐cut distinction between particular groups of ordinary chondrites is only possible for group H, while distinguishing L chondrites from LL chondrites is not always obvious. The results of the statistical analyses relating to the question of the possible existence of several primordial parent bodies (formation environments) of each group of ordinary chondrites are consistent with the results of contemporary astronomical spectroscopy research. What is particularly interesting is obtaining indications of the existence of common formation environments of the matter of L and LL chondrites, possibly on a few primordial parent bodies. The statistical analyses indicate that there is no correlation between the concentration of principal chemical components and the petrographic type of ordinary chondrites. This proves homogenous distributions of these elements within the parent bodies of each group of ordinary chondrites. Hence, the distribution of these elements in individual present‐day asteroids is also homogenous. [ABSTRACT FROM AUTHOR]

Sarah Frances Whiting developed innovative and influential laboratory work in her introductory astronomy classes at Wellesley College in the late 1800s and early 1900s. Whiting was strongly influenced by Edward Pickering and the early physics laboratory education at the Massachusetts Institute of Technology. This article explores the early development of laboratory work in astronomy education at Wellesley and Whiting's underlying philosophy of education. By laboratory work, Whiting meant day-time work, including work with astronomical photographs and spectroscopy. Her pedagogy was encapsulated in her phrase "to sharpen the pencil sharpens the mind," which referenced the importance of a student's familiarity with tools as well as the role of drawing in astronomical work. Whiting further modeled her instruction after the work being conducted at the Harvard College Observatory in order to prepare her students for potential future employment as astronomers. [ABSTRACT FROM AUTHOR]

We present Gran Telescopio Canarias (GTC) spectroscopic confirmations of 55 faint Planetary Nebulae (PNe) candidates discovered largely in the INT Photometric H α Survey (IPHAS) of the Northern Galactic Plane by our pro-am collaboration. We confirm 46 of them as 'True' (T), 4 as 'Likely' (L), and 5 as 'Possible' (P) PNe and including 5 new PNe central star (CSPN) discoveries. This was from observations of 62 new candidates yielding a maximum PN discovery success rate of 89 per cent. The sensitivity and longer wavelength coverage of IPHAS allows PNe to be found in regions of greater extinction and at these lower Galactic latitudes, including PNe in a more advanced evolutionary state and at larger distances compared to previously known Galactic PNe. We use a holistic set of observed characteristics and optical emission-line diagnostics to confirm candidates. Plasma properties have been determined in a self-consistent way using pyneb. This work is facilitated by the functionality of our powerful, multiwavelength database 'HASH' (Hong Kong, Australian Astronomical Observatory, Strasbourg Observatory H-alpha Planetary Nebula catalogue) that federates known imaging, spectroscopy, and other pertinent data for all Galactic T, L, P PNe, and the significant numbers of mimics. Reddenings, corrected radial velocities, and PNe electron density and temperature estimates are provided for these new PNe wherever possible. [ABSTRACT FROM AUTHOR]

The recent interstellar detection of cyanonaphthalenes brings interest in related aromatic molecular species that could be present in similar astronomical environments. In this context, ethynyl derivatives of naphthalene are promising candidates to be observed in the Taurus Molecular Cloud (TMC-1), where cyanonaphthalenes together with cyano- and ethynyl-derivatives of cyclopentadiene and benzene have been detected. To enable the interstellar searches for ethynyl derivatives of naphthalene, their pure rotational spectra need to be investigated in the laboratory. We have observed for the first time the rotational spectra of 1- and 2-ethynylnaphthalene species using a broad-band Fourier-transform microwave spectrometer operating in the 2–8 GHz frequency region. Accurate spectroscopic parameters are derived from the analysis of the experimental spectra, allowing for reliable predictions for astronomical searches. Our searches in TMC-1 for both isomers provide upper limits for the abundances of these species. [ABSTRACT FROM AUTHOR]

We introduce the scientific motivations for the development of the Cassegrain U-Band Efficient Spectrograph (CUBES) that is now in construction for the Very Large Telescope. The assembled cases span a broad range of contemporary topics across Solar System, Galactic and extragalactic astronomy, where observations are limited by the performance of current ground-based spectrographs shortwards of 400 nm. A brief background to each case is presented and specific technical requirements on the instrument design that flow-down from each case are identified. These were used as inputs to the CUBES design, that will provide a factor of ten gain in efficiency for astronomical spectroscopy over 300-405 nm, at resolving powers of R ∼ 24,000 and ∼ 7,000. We include performance estimates that demonstrate the ability of CUBES to observe sources that are up to three magnitudes fainter than currently possible at ground-ultraviolet wavelengths, and we place its predicted performance in the context of existing facillities. [ABSTRACT FROM AUTHOR]

To decode the information stored within a spectrum, detailed modelling of the physical state is required together with accurate radiative transfer solution schemes. In the analysis of stellar spectra, the numerical model often needs to account for high velocity outflows, multi-dimensional structures, and the effects of binary companions. Focusing now on binary systems, we present the BOSS-3D spectral synthesis code, which is capable of calculating synthetic line profiles for a variety of binary systems. Assuming the state of the circumstellar material to be known, the standard pz -geometry is extended by defining individual coordinate systems for each object. By embedding these coordinate systems within the observer's frame, BOSS-3D automatically accounts for outflows or discs within both involved systems, and includes all Doppler shifts. Moreover, the code accounts for different length-scales, and thus could also be used to analyse transit-spectra of planetary atmospheres. As a first application of BOSS-3D, we model the phase-dependent line profiles for the enigmatic binary (or multiple) system LB-1. [ABSTRACT FROM AUTHOR]

Changes in the supercycle lengths of some SU UMa-type dwarf novae have been detected by other studies, and indicate that the mass transfer rates noticeably decrease over time. We investigated the supercycle lengths of three SU UMa-type dwarf novae: AR Pic, QW Ser, and V521 Peg, to determine if they have detectable changes in their supercycles. We present the results of optical spectroscopic and photometric observations of these sources. Our observations were conducted in 2016 and 2017 at the Boyden Observatory and the Sutherland station of the South African Astronomical Observatory. The quiescent results indicated that all three sources are typical SU UMa-type dwarf novae. We also present results of AR Pic and QW Ser in outburst and of V521 Peg during a precursor outburst and superoutburst. Light curves were supplemented by the Catalina Real-Time Transient Survey, the ASAS-3 and ASAS-SN archives, and the AAVSO International Database in order to investigate the long-term behaviour of these sources. Our results combined with catalogued properties for all short-period dwarf novae show a possible relationship between the supercycle time in SU UMa systems and their orbital periods, which is interpreted as the decline in the mass transfer rate as systems evolve towards and away from the 'period minimum'. At the shortest orbital periods, SU UMa systems are almost indistinguishable from WZ Sge systems. However, we propose that the scaleheight between the secondary's photosphere and L1 may be a factor that distinguish the SU UMa subclasses. [ABSTRACT FROM AUTHOR]

Space domain awareness (SDA) is becoming more important with a constantly increasing number of artificial objects in space. Astronomical reflectance spectroscopy (ARS) is a promising technique employed for remote characterization of space objects. In geosynchronous earth orbit (GEO), the chemical characteristics of a material change continuously, as it is exposed to the harsh radiation environment of several damaging species (with electrons being the primary damaging species in terms of energy deposition). These chemical modifications alter the light absorbed by and reflected from the object at certain wavelengths, resulting in a concomitant change of the measured object’s brightness and color index. By understanding the evolution of the color index of a material as a function of time on orbit, ARS can become a powerful tool for remote characterization of space objects as well as anomaly characterization and resolution. In this study, we investigate the effect of a space-simulated environment represented by high-energy (100 keV) electrons on the evolution of optical properties of several spacecraft-relevant polymer materials. [ABSTRACT FROM AUTHOR]

The kinetics of the reactions of tributylphosphine with allenic and olefinic Michael acceptors in dichloromethane at 20 °C was followed by photometric and NMR spectroscopic methods. Combination with DFT-calculated methyl anion affinities revealed the relevance of retroaddition barriers in phosphine-catalysed reactions when mixtures of allenic and olefinic substrates are used. [ABSTRACT FROM AUTHOR]

The number of known variable stars has increased by several magnitudes over the last decade, and automated classification routines are becoming increasingly important to cope with this development. Here we show that the 'upside-down CBH variables', which were proposed as a potentially new class of variable stars by Heinze et al. in the ATLAS First Catalogue of Variable Stars, are, at least to a high percentage, made up of α2 Canum Venaticorum (ACV) variables – that is, photometrically variable magnetic chemically peculiar (CP2/He-peculiar) stars – with distinct double-wave light curves. Using suitable selection criteria, we identified 264 candidate ACV variables in the ATLAS variable star catalogue. 62 of these objects were spectroscopically confirmed with spectra from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (all new discoveries except for nine stars) and classified on the MK system. The other 202 stars are here presented as ACV star candidates that require spectroscopic confirmation. The vast majority of our sample of stars are main-sequence objects. Derived masses range from 1.4 M⊙ to 5 M⊙, with half our sample stars being situated in the range from 2 M⊙ to 2.4 M⊙, in good agreement with the spectral classifications. Most stars belong to the thin or thick disc; four objects, however, classify as members of the halo population. With a peak magnitude distribution at around 14th magnitude, the here presented stars are situated at the faint end of the known Galactic mCP star population. Our study highlights the need to consider rare variability classes, like ACV variables, in automated classification routines. [ABSTRACT FROM AUTHOR]

We use the statistical power of the MaNGA integral-field spectroscopic galaxy survey to improve the definition of strong line diagnostic boundaries used to classify gas ionization properties in galaxies. We detect line emission from 3.6 million spaxels distributed across 7400 individual galaxies spanning a wide range of stellar masses, star formation rates, and morphological types, and find that the gas-phase velocity dispersion σHα correlates strongly with traditional optical emission-line ratios such as [S ii ]/Hα, [N ii ]/Hα, [O i ]/Hα, and [O iii ]/Hβ. Spaxels whose line ratios are most consistent with ionization by galactic H ii regions exhibit a narrow range of dynamically cold line-of-sight velocity distributions (LOSVDs) peaked around 25 km s−1 corresponding to a galactic thin disk, while those consistent with ionization by active galactic nuclei (AGNs) and low-ionization emission-line regions (LI(N)ERs) have significantly broader LOSVDs extending to 200 km s−1. Star-forming, AGN, and LI(N)ER regions are additionally well separated from each other in terms of their stellar velocity dispersion, stellar population age, Hα equivalent width, and typical radius within a given galaxy. We use our observations to revise the traditional emission-line diagnostic classifications so that they reliably identify distinct dynamical samples both in two-dimensional representations of the diagnostic line ratio space and in a multidimensional space that accounts for the complex folding of the star-forming model surface. By comparing the MaNGA observations to the SDSS single-fiber galaxy sample, we note that the latter is systematically biased against young, low-metallicity star-forming regions that lie outside of the 3″ fiber footprint. [ABSTRACT FROM AUTHOR]

We present spectroscopic and photometric observations of 17 dwarf-nova superoutbursts obtained by KOOLS-IFU mounted on the 3.8 m telescope Seimei at the Okayama Observatory of Kyoto University and through the Variable Star Network collaboration (VSNET). Our spectroscopic observations for six outbursts were performed within 1 d of their optical peak. 11 objects (TCP J00590972+3438357, ASASSN-19ado, TCP J06073081−0101501, ZTF20aavnpug, ASASSN-19ady, MASTER OT J061642.05+435617.9, TCP J20034647+1335125, ASASSN-20kv, ASASSN-20kw, MASTER OT J213908.79+161240.2, and ASASSN-20mf) were previously unknown systems, and our observations enabled quick classification of their transient type. These results illustrate that the Seimei telescope has the capability to conduct quick follow-up observations of unknown transients. Our photometric observations yielded that 11 of the objects are WZ Sge-type dwarf novae and their candidates, and the other six are SU UMa-type dwarf novae and their candidates. The He  ii 4686 Å emission line was clearly detected among ASASSN-19ado, TCP J06073081−0101501 and MASTER OT J213908.79+161240.2, the association of which with a spiral arm structure in an accretion disk has been suggested in previous studies. Our result suggests that a higher-inclination system shows a stronger emission line of He  ii 4686 Å, as well as larger-amplitude early superhumps. [ABSTRACT FROM AUTHOR]

Enabling efficient injection of light into single-mode fibres (SMFs) is a key requirement in realizing diffraction-limited astronomical spectroscopy on ground-based telescopes. SMF-fed spectrographs, facilitated by the use of adaptive optics (AO), offer distinct advantages over comparable seeing-limited designs, including higher spectral resolution within a compact and stable instrument volume, and a telescope independent spectrograph design. iLocater is an extremely precise radial velocity (EPRV) spectrograph being built for the Large Binocular Telescope (LBT). We have designed and built the front-end fibre injection system, or acquisition camera, for the SX (left) primary mirror of the LBT. The instrument was installed in 2019 and underwent on-sky commissioning and performance assessment. In this paper, we present the instrument requirements, acquisition camera design, as well as results from first-light measurements. Broad-band SMF coupling in excess of 35 per cent (absolute) in the near-infrared (0.97–1.31  |${\mu {\rm m}}$|⁠) was achieved across a range of target magnitudes, spectral types, and observing conditions. Successful demonstration of on-sky performance represents both a major milestone in the development of iLocater and in making efficient ground-based SMF-fed astronomical instruments a reality. [ABSTRACT FROM AUTHOR]

The identification of the carriers of the absorption features associated with the diffuse interstellar bands (DIBs) is a long-standing problem in astronomical spectroscopy. Computational simulations can contribute to the assignment of the carriers of DIBs since variations in molecular structure and charge state can be studied more readily than through experimental measurements. Polyaromatic hydrocarbons have been proposed as potential carriers of these bands, and it is shown that simulations based upon density functional theory and time-dependent density functional theory calculations can describe the vibrational structure observed in experiment for neutral and cationic naphthalene and pyrene. The vibrational structure arises from a small number of vibrational modes involving in-plane atomic motions, and the Franck–Condon–Herzberg–Teller approximation improves the predicted spectra in comparison with the Franck–Condon approximation. The study also highlights the challenges for the calculations to enable the assignment in the absence of experimental data, namely prediction of the energy separation between the different electronic states to a sufficient level of accuracy and performing vibrational analysis for higher-lying electronic states. [ABSTRACT FROM AUTHOR]

This elementary review covers the basics of working with astronomical data, notably with images, spectra and higher-level (catalog) data. The basic concepts and tools are presented using both application software (DS9 and TOPCAT) and Python. The level of presentation is suitable for undergraduate students, but should also be accessible to advanced high school students.

The interstellar presence of protonated nitrous oxide has been suspected for some time. Using established high-accuracy quantum chemical techniques, spectroscopic constants and fundamental vibrational frequencies are provided for the lower energy O-protonated isomer of this cation and its deuterated isotopologue. The vibrationally-averaged B0 and C0 rotational constants are within 6 MHz of their experimental values and the DJ quartic distortion constants agree with experiment to within 3%. The known gas phase O-H stretch of NNOH+ is 3330.91 cm-1, and the vibrational configuration interaction computed result is 3330.9 cm-1. Other spectroscopic constants are also provided, as are the rest of the fundamental vibrational frequencies for NNOH+ and its deuterated isotopologue. This high-accuracy data should serve to better inform future observational or experimental studies of the rovibrational bands of protonated nitrous oxide in the interstellar medium and the laboratory. [ABSTRACT FROM AUTHOR]

The spectrum of dicarbon (C2) is important in astrophysics and for spectroscopic studies of plasmas and flames. The C2 spectrum is characterized by many band systems with new ones still being actively identified; astronomical observations involve eight of these bands. Recently, Furtenbacher et al. presented a set of 5699 empirical energy levels for 12C2, distributed among 11 electronic states and 98 vibronic bands, derived from 42 experimental studies and obtained using the MARVEL (Measured Active Rotational-Vibrational Energy Levels) procedure. Here, we add data from 13 new sources and update data from 5 sources. Many of these data sources characterize high-lying electronic states, including the newly detected 3 3Πg state. Older studies have been included following improvements in the MARVEL procedure that allow their uncertainties to be estimated. These older works in particular determine levels in the C 1Πg state, the upper state of the insufficiently characterized Deslandres–d'Azambuja (C 1Πg–A 1Πu) band. The new compilation considers a total of 31 323 transitions and derives 7047 empirical (marvel) energy levels spanning 20 electronic and 142 vibronic states. These new empirical energy levels are used here to update the 8states C2 ExoMol line list. This updated line list is highly suitable for high-resolution cross-correlation studies in astronomical spectroscopy of, for example, exoplanets, as 99.4 per cent of the transitions with intensities over 10−18 cm molecule−1 at 1000 K have frequencies determined by empirical energy levels. [ABSTRACT FROM AUTHOR]

The spectrum of dicarbon (C2) is important in astrophysics and for spectroscopic studies of plasmas and flames. The C2 spectrum is characterized by many band systems with new ones still being actively identified; astronomical observations involve eight of these bands. Recently, Furtenbacher et al. presented a set of 5699 empirical energy levels for 12C2, distributed among 11 electronic states and 98 vibronic bands, derived from 42 experimental studies and obtained using the MARVEL (Measured Active Rotational-Vibrational Energy Levels) procedure. Here, we add data from 13 new sources and update data from 5 sources. Many of these data sources characterize high-lying electronic states, including the newly detected 3 3Πg state. Older studies have been included following improvements in the MARVEL procedure that allow their uncertainties to be estimated. These older works in particular determine levels in the C 1Πg state, the upper state of the insufficiently characterized Deslandres–d'Azambuja (C 1Πg–A 1Πu) band. The new compilation considers a total of 31 323 transitions and derives 7047 empirical (marvel) energy levels spanning 20 electronic and 142 vibronic states. These new empirical energy levels are used here to update the 8states C2 ExoMol line list. This updated line list is highly suitable for high-resolution cross-correlation studies in astronomical spectroscopy of, for example, exoplanets, as 99.4 per cent of the transitions with intensities over 10−18 cm molecule−1 at 1000 K have frequencies determined by empirical energy levels. [ABSTRACT FROM AUTHOR]

Optical fibers have altered astronomical instrument design by allowing for a complex, often large instrument to be mounted in a remote and stable location with respect to the telescope. The fibers also enable the possibility to rearrange the signal from a focal plane to form a psuedo-slit at the entrance to a spectrograph, optimizing the detector usage and enabling the study of hundreds of thousands of stars or galaxies simultaneously. Multi-core fibers in particular offer several favorable properties with respect to traditional fibers: 1) the separation between single-mode cores is greatly reduced and highly regular with respect to free standing fibers, 2) they offer a monolithic package with multi-fiber capabilities and 3) they operate at the diffraction limit. These properties have enabled the realization of single component photonic lanterns, highly simplified fiber Bragg gratings, and advanced fiber mode scramblers. In addition, the precise grid of cores has enabled the design of efficient single-mode fiber integral field units for spectroscopy. In this article, we provide an overview of the broad range of applications enabled by multi-core fiber technology in astronomy and outline future areas of development. [ABSTRACT FROM AUTHOR]

The problem of denoising a 1D signal possessing varying degrees of smoothness is ubiquitous in time-domain astronomy and astronomical spectroscopy. For example, in the time domain, an astronomical object may exhibit a smoothly varying intensity that is occasionally interrupted by abrupt dips or spikes. Likewise, in the spectroscopic setting, a noiseless spectrum typically contains intervals of relative smoothness mixed with localized higher frequency components such as emission peaks and absorption lines. In this work, we present trend filtering, a modern non-parametric statistical tool that yields significant improvements in this broad problem space of denoising spatially heterogeneous signals. When the underlying signal is spatially heterogeneous, trend filtering is superior to any statistical estimator that is a linear combination of the observed data – including kernel smoothers, LOESS, smoothing splines, Gaussian process regression, and many other popular methods. Furthermore, the trend filtering estimate can be computed with practical and scalable efficiency via a specialized convex optimization algorithm, e.g. handling sample sizes of n ≳ 107 within a few minutes. In a companion paper, we explicitly demonstrate the broad utility of trend filtering to observational astronomy by carrying out a diverse set of spectroscopic and time-domain analyses. [ABSTRACT FROM AUTHOR]

An isotopic-independent, highly accurate potential energy surface (PES) has been determined for CO2 by refining a purely ab initio PES with selected, purely experimentally determined rovibrational energy levels. The purely ab initio PES is denoted Ames-0, while the refined PES is denoted Ames-1. Detailed tests are performed to demonstrate the spectroscopic accuracy of the Ames-1 PES. It is shown that Ames-1 yields σrms (root-mean-squares error) = 0.0156 cm-1 for 6873 J = 0-117 12C16O2 experimental energy levels, even though less than 500 12C16O2 energy levels were included in the refinement procedure. It is also demonstrated that, without any additional refinement, Ames-1 yields very good agreement for isotopologues. Specifically, for the 12C16O2 and 13C16O2 isotopologues, spectroscopic constants Gv computed from Ames-1 are within ±0.01 and 0.02 cm-1 of reliable experimentally derived values, while for the 16O12C18O, 16O12C17O, 16O13C18O, 16O13C17O, 12C18O2, 17O12C18O, 12C17O2, 13C18O2, 13C17O2, 17O13C18O, and 14C16O2 isotopologues, the differences are between ±0.10 and 0.15 cm-1. To our knowledge, this is the first time a polyatomic PES has been refined using such high J values, and this has led to new challenges in the refinement procedure. An initial high quality, purely ab initio dipole moment surface (DMS) is constructed and used to generate a 296 K line list. For most bands, experimental IR intensities are well reproduced for 12C16O2 using Ames-1 and the DMS. For more than 80% of the bands, the experimental intensities are reproduced with σrms(ΔI) < 20% or σrms(ΔI/δobs) < 5. A few exceptions are analyzed and discussed. Directions for future improvements are discussed, though it is concluded that the current Ames-1 and the DMS should be useful in analyzing and assigning high-resolution laboratory or astronomical spectra. [ABSTRACT FROM AUTHOR]

The three lowest (12A′, 22A′, and 12A″) potential-energy surfaces of the C2Cl radical, correlating at linear geometries with 2Σ+ and 2Π states, have been studied ab initio using a large basis set and multireference configuration-interaction techniques. The electronic ground state is confirmed to be bent with a very low barrier to linearity, due to the strong nonadiabatic electronic interactions taking place in this system. The rovibronic energy levels of the 12C12C35Cl isotopomer and the absolute absorption intensities at a temperature of 5 K have been calculated, to an upper limit of 2000 cm-1, using diabatic potential-energy and dipole moment surfaces and a recently developed variational method. The resulting vibronic states arise from a strong mixture of all the three electronic components and their assignments are intrinsically ambiguous. [ABSTRACT FROM AUTHOR]