Atlas of new and revised high-resolution spectroscopy of six CO isotopologues in the 101–115 nm range

Abstract

Atlas of new and revised high-resolution spectroscopy of six COisotopologues in the 101-115 nm range Transition energies of the u = 0, 1, 2, and 3 to u = 0 bands of the B 1 Σ + , C 1 Σ + , and E 1 Π to X 1 Σ + states, related term values, and molecular constants ABSTRACT Our knowledge of astronomical environments containing CO depends on accurate molecular data to reproduce and interpret observed spectra. The recent and future improvements of ultraviolet space instrumentation, both in sensitivity and resolution, require increasingly detailed laboratory molecular spectroscopy as a reference. As part of a long-term experimental campaign at the SOLEIL Synchrotron facility, we have acquired gas-phase absorption spectra of six CO isotopologues in the vacuum ultraviolet. These spectra are recorded using the Fourier-transform spectrometer installed on the DESIRS beamline, providing a unique resolving power up to 10 6 in the 8-13 eV range. We have used resolutions in the 300 000-450 000 range for this campaign, which enable the analysis of individual line positions. We report new measurements on neighboring Rydberg states in the 101-115 nm range that could also be used as f -value calibrators, namely B 1 Σ + , C 1 Σ + , and E 1 Π, for six CO isotopologues. This range encompasses the absorption transitions B(v = 0, 1, and 2), C(v = 0, 1, 2, and 3), and E(v = 0, 1, 2, and 3) from X 1 Σ + (v = 0). Higher resolution laser-based measurements of CO isotopologues from the literature are used to improve the absolute calibration and accuracy of our data. The overall uncertainty of the great majority of the line positions presented in this atlas is estimated to be 0.01 cm −1 . In addition, some of the data derived from transition energies measurements, such as term values and molecular constants, are obtained for the first time, and others are improvements on previous sparser or lower spectral resolution datasets.Article published by EDP Sciences A114, page 1 of 62 A&A 614, A114 (2018) A114, page 3 of 62 A&A 614, A114 (2018) Laser calibration benchmarks and associated dataAn absolute calibration of lines requires the availability of accurately determined standards, either atomic or molecular, as close as possible to the lines under study. There are many reported laser-based measurements of CO VUV transitions with accurate absolute calibrations based on primary standards. Some previous work has been limited to a few lines of each vibrational band, while others offer almost complete bands for use as comparisons for calibration purposes. Data like this exist for most CO isotopologues. They are summarized in detail in this section. Reports of laser-based measurements that were used to accurately calibrate our spectra often also presented an analysis of the rotational structure of the bands under study, providing associated data such as term values, reduced term values, and molecular constants. These results are also mentioned in detail in this section as they are compared later to our own results.Depending on the data available, laser...

High-resolution Fourier-transform spectroscopy and deperturbation analysis of the A1Π(v = 1) level in 12C18O

“…The updated frequency calibration described above lead to an increase of all frequencies by 0.01 cm −1 . Our analysis of the B ← − X and C ← − X absorption bands improves upon the similar experimental study of Lemaire et al [32] , also using the DESIRS beamline. This re-analysis was necessary in order that these bands are known with a precision matching our measured VIS-FT B → A and C → A line frequencies (having uncertainties down to 0.005 cm −1 ) and sufficient to resolve the local line shifts due to energy level perturbations affecting B( v ) and C(1) levels.…”

“…Higher-J rotational levels than previously analysed are present in the new high-temperature absorption spectra. We also find overall energy shifts for the B(0), B(1), and C(0) vibrational levels relative to Lemaire et al [32] , of -0.05, -0.05, and 0.025 cm −1 , respectively, based on an absolute frequency calibration using the Xe reference data described above and benefiting from the simultaneous self-consistent fitting of overlapping spectra covering all bands. Small irregularities in the level energy progressions of 12 C 18 O B 1 + ( v = 0, 1) and C 1 + ( v = 0) levels are indicated in Fig.…”

“…The detection of CO and determination of its local density and temperature are essential for modelling the beginning of stellar evolution, the dynamics of interstellar clouds and nebulae, the atmospheres of planets and exoplanets, the characterisation of extra-galactic clouds, and the search for varying fundamental constants in the early Uni-Janji ć et al [24] ; and the K ępa-Rytel system (E 1 -A 1 ) by K ępa et al [25] and K ępa [20] . The other band systems investigated for the 12 C 18 O isotopologue are: 4 th Positive (A 1 -X 1 + ) [22,[26][27][28][29] ; Hopfield-Birge (B 1 + -X 1 + ) [22,27,[30][31][32][33] , C 1 + -X 1 + [27, [31][32][33][34][35] , E 1 -X 1 + [26,[31][32][33]36] , and C 1 + -B 1 + [37] .…”

Strong and selective isotope effect in the vacuum ultraviolet photodissociation branching ratios of carbon monoxide

“…Now it is generally agreed that self-shielding effect is the main reason of the massive isotope fractionation observed in the above experiment and also that in the solar system, while Thiemens´ experiment does have the effect of encouraging people to include the different photoabsorption and photodissociation cross sections for different CO isotopologues in their models, which has been proved to make the modeling results in closer agreement with the experimental measurements 17,18 . Compared to the absorption line positions, accurate absolute values of photoabsorption and photodissociation cross sections are much more difficult to be measured, thus continued recent efforts are being devoted to obtain more precise values of these for all the CO isotopologues in hope of further improving the photochemical modeling 19–22 .…”

Photodissociation branching ratios of 13C16O and 12C18O in the vacuum ultraviolet region from 107 800 to 109 700 cm−1

“…Whole spectroscopic studies have been devoted to characterizing the molecular parameters of all CO isotopologs so that the astronomical observations can be better interpreted and to further improve the photochemical modeling (Eidelsberg & Rostas 1990;Eidelsberg et al 1991Eidelsberg et al , 1992Eidelsberg et al , 2004Eidelsberg et al , 2006Eidelsberg et al , 2012Eidelsberg et al , 2014Eidelsberg et al , 2017Eikema et al 1994;Ubachs et al 1994;Stark et al 2014;Lemaire et al 2018), but very few studies have discussed the subsequent "trapping reactions" following the VUV photodestruction process of CO (Clayton 2011;Shi et al 2017;Lyons et al 2018). Recently, Lyons et al (2018) reanalyzed the ATMOS FTS data and found that the heavy C isotope ( 13 C) is also depleted in the Sun compared with that in the Earth and other planetary objects.…”