arXiv subjects

Sven Thorwirth

Publications and source records attributed to Sven Thorwirth.

15 recordsLinked to original sources

arXiv2026

Spectroscopic Detection and Characterization of Cyanooxomethylium, NCCO$^+$

Cyanooxomethylium, NCCO$^+$, a fundamental linear acylium ion, has been observed spectroscopically for the first time using action spectroscopy in ion trap apparatuses. A first low-resolution infrared spectrum was obtained between 500 to 1400 cm$^{-1}$ and 2000 to 2500 cm$^{-1}$ using the Free Electron Laser for Infrared eXperiments (FELIX) and the FELion apparatus, employing infrared predissociation of the weakly bound NCCO$^+$-Ne complex. Subsequently, high-resolution studies of the bare ion were performed with the COLtrap II setup, one targeted at the CN-stretching mode $\nu_2$ around 2150 cm$^{-1}$ using leak-out spectroscopy and one at the pure rotational spectrum employing a leak-out infrared/millimeter-wave double resonance approach covering transition frequencies as high as 246 GHz. Spectroscopic detection and analysis were guided by high-level quantum-chemical calculations performed at the CCSD(T) level of theory. The collected data permit accurate frequency predictions to support future astronomical searches with sensitive radio telescopes.

physics.chem-ph↗

arXiv2026

High-Resolution Infrared Spectroscopy and ASAP Analysis of Cyclopentadiene: The Vibrational Modes below 860 cm$^{-1}$ and the ${\nu}_{21}$ Mode at 961 cm$^{-1}$

The spectroscopic fingerprints of vibrationally excited states of astronomical molecules are interesting for multiple reasons. They are excellent temperature probes of the corresponding astronomical regions and are thought to be the origin of many unknown lines in astronomical survey spectra. Rovibrational spectra provide accurate vibrational energies and can guide subsequent pure rotational studies. The Automated Spectral Assignment Procedure (ASAP) greatly simplifies the rovibrational analysis when the rotational spectrum of either the upper or lower vibrational state is known with a high degree of accuracy (e.g., from a rotational analysis). Here, we present a new implementation of ASAP for the analysis of cyclopentadiene, a cyclic pure hydrocarbon that has already been detected astronomically toward the cold core of the Taurus Molecular Cloud. Using the synchrotron radiation extracted by the AILES beamline of the SOLEIL facility, we recorded mid- and far-infrared high-resolution spectra of cyclopentadiene. We analyzed the rovibrational spectrum of the $\nu_{21}$ fundamental (961 cm$^{-1}$) with ASAP and used ASAP$^2$ to determine the vibrational energies of the eight vibrational modes below 860 cm$^{-1}$. ASAP$^2$ is an extension of ASAP for rovibrational bands where the rotational structures of the lower and upper states are known with high accuracy, leaving only the vibrational band center to be determined. The presented rovibrational fingerprints agree with the results from pure rotational spectroscopy, demonstrating the efficiency and reliability of our new ASAP implementation.

physics.chem-ph↗

arXiv2025

Leveraging MMW-MMW Double Resonance Spectroscopy to Understand the Pure Rotational Spectrum of Glycidaldehyde and 17 of Its Vibrationally Excited States

Broadband measurements of glycidaldehyde in the frequency ranges 75-170 and 500-750 GHz were recorded to extend previous analyses of its pure rotational spectrum in the microwave region. The rotational parameters of the ground vibrational states for the main isotopologue and the three singly 13C-substituted isotopologues were considerably improved, and additional higher-order parameters were determined. To identify new vibrationally excited states in the dense and convoluted spectrum, an updated version of the double-modulation double-resonance spectroscopy technique was used. Connecting transitions with a shared energy level into series and expanding these via Loomis-Wood plots proved to be a powerful method, which allowed the identification of 11 new vibrationally excited states in addition to the already known aldehyde torsions, v21 = 1 to v21 = 6. Interactions between several vibrational states were observed, and three interacting systems were treated successfully. Rotational transitions of glycidaldehyde were searched for in the imaging spectral line survey ReMoCA obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the high-mass star-forming region Sgr B2(N). The observed spectra were modeled under the assumption of local thermodynamic equilibrium (LTE). Glycidaldehyde, an oxirane derivative, was not detected toward Sgr B2(N2b). The upper limit on its column density implies that it is at least six times less abundant than oxirane in this source.

physics.chem-ph↗

arXiv2025

Extending the rotational spectrum of cyclopentadiene towards higher frequencies and vibrational states

Cyclopentadiene (c-C5H6) is a cyclic pure hydrocarbon that was already detected astronomically towards the prototypical dark cloud TMC-1 (Cernicharo et al. 2021, Astron. Astrophys. 649, L15). However, accurate predictions of its rotational spectrum are still limited to the microwave region and narrow quantum number ranges. In the present study, the pure rotational spectrum of cyclopentadiene was measured in the frequency ranges 170-250 GHz and 340-510 GHz to improve the number of ground vibrational state assignments by more than a factor of 20, resulting in more accurate rotational parameters and the determination of higher-order centrifugal distortion parameters. Additionally, vibrational satellite spectra of cyclopentadiene in its eight energetically lowest vibrationally excited states were analyzed for the first time. Coriolis interactions between selected vibrational states were identified and treated successfully in combined fits. Previous microwave work on the three singly 13C substituted isotopologues was extended significantly also covering frequency ranges up to 250 GHz. The new data sets permit reliable frequency predictions for the isotopologues and vibrational satellite spectra far into the sub-mm-wave range. Finally, the experimental rotational constants of all available isotopologues and calculated zero-point vibrational contributions to the rotational constants were used to derive a semi-experimental equilibrium structure of this fundamental ring molecule.

physics.chem-ph↗

arXiv2024

Millimeter-millimeter-wave double-modulation double-resonance spectroscopy

A new millimeter- to millimeter-wave double-modulation double-resonance (MMW-MMW DM-DR) scheme has been applied to record spectra of two astronomically relevant complex organic molecules (COMs), propanal (C2H5CHO) and ethyl cyanide (C2H5CN), to demonstrate advantages of the DM-DR experimental technique. The DR technique helps to identify target transitions in a forest of lines and the implementation of a DM procedure (modulation of the pump and probe source) allows for confusion- and baseline-free spectra containing only the line(s) of interest. In particular the unambiguous assignment of weak and blended transitions in very dense MMW spectra is highlighted. Details of the observed Autler-Townes line splitting and possible future applications, such as automated analyses and adaptions of DM-DR methods to other experimental setups, are discussed.

physics.chem-ph↗

arXiv2024

On the spectroscopy of phosphaalkynes: Millimeter- and submillimeter wave study of C2H5CP

Ethyl phosphaethyne, C2H5CP, has been characterized spectroscopically in the gas phase for the first time, employing millimeter- and submillimeter-wave spectroscopy in the frequency regime from 75 to 760 GHz. Spectroscopic detection and analysis was guided by high-level quantum-chemical calculations of molecular structures and force fields performed at the coupled-cluster singles and doubles level extended by a perturbative correction for the contribution from triple excitations, CCSD(T), in combination with large basis sets. Besides the parent isotopologue, the singly substituted 13C species were observed in natural abundance up to frequencies as high as 500 GHz. Despite the comparably low astronomical abundance of phosphorus, phosphaalkynes, R--CP, such as C2H5CP are promising candidates for future radio astronomical detection.

physics.chem-ph↗

arXiv2024

Formation of the Methyl Cation by Photochemistry in a Protoplanetary Disk

Forty years ago it was proposed that gas phase organic chemistry in the interstellar medium was initiated by the methyl cation CH3+, but hitherto it has not been observed outside the Solar System. Alternative routes involving processes on grain surfaces have been invoked. Here we report JWST observations of CH3+ in a protoplanetary disk in the Orion star forming region. We find that gas-phase organic chemistry is activated by UV irradiation.

astro-ph.GA↗

arXiv2022

Leak-out Spectroscopy, a universal method of action spectroscopy in cold ion traps

A novel method of spectroscopy in ion traps termed leak-out spectroscopy (LOS) is presented. Here, mass selected, cold ions are excited by an infrared laser. In a subsequent collision with a neutral buffer gas particle their internal energy is then transferred to kinetic energy. As a result, these ions leak out from the ion trap and are detected. The LOS scheme is generally applicable, very sensitive and close to background free when operated at low temperature. The potential of this method is demonstrated and characterized here for the first time by recording the rotationally resolved spectrum of the C-H stretching vibration $ν_1$ of linear C$_3$H$^+$. Besides performing high-resolution spectroscopy, this method opens up the way for analyzing the composition of trap content, e.g., determining isomer ratios, by selectively expelling isomers or other isobaric ions from the trap. Likewise, LOS can be used to prepare clean samples of structural and nuclear spin isomers.

physics.chem-ph↗

arXiv2021

(Sub-)millimeter-wave spectroscopy of gauche-propanal

A detailed analysis of (sub-)millimeter-wave spectra of the vibrational ground state ($\upsilon=0$) combined with the energetically lowest excited vibrational state ($\upsilon_{24}=1$; aldehyde torsion) of gauche-propanal (g-C$_2$H$_5$CHO) up to 500 GHz is presented. Both vibrational states, $\upsilon=0$ and $\upsilon_{24}=1$, are treated with tunneling rotation interactions between their two respective tunneling states, which originate from two stable degenerate gauche-conformers; left- and right-handed configurations separated by a small potential barrier. Thanks to double-modulation double-resonance (DM-DR) measurements, important but weak $c$-type transitions connecting the tunneling states could be unambiguously assigned. In addition, Coriolis interaction as well as Fermi resonance between the two vibrational states needed to be taken into account to derive fits with experimental accuracy using Pickett's SPFIT program in a reduced axis system (RAS). Based on the rotational analysis, the fundamental vibrational frequency $ν_{24}$ of gauche-propanal is redetermined to 68.75037(30) cm$^{-1}$.

physics.chem-ph↗

arXiv2021

High-resolution infrared action spectroscopy of the fundamental vibrational band of CN+

Rotational-vibrational transitions of the fundamental vibrational modes of the $^{12}$C$^{14}$N$^+$ and $^{12}$C$^{15}$N$^+$ cations have been observed for the first time using a cryogenic ion trap apparatus with an action spectroscopy scheme. The lines P(3) to R(3) of $^{12}$C$^{14}$N$^+$ and R(1) to R(3) of $^{12}$C$^{15}$N$^+$ have been measured, limited by the trap temperature of approximately 4 K and the restricted tuning range of the infrared laser. Spectroscopic parameters are presented for both isotopologues, with band origins at 2000.7587(1) and 1970.321(1) cm$^{-1}$, respectively, as well as an isotope independent fit combining the new and the literature data.

physics.chem-ph↗

arXiv2020

Rotational spectroscopy of singly $^{13}$C substituted isotopomers of propyne and determination of a semi-empirical equilibrium structure

Submillimeter spectra of three isotopomers of propyne containing one $^{13}$C atom were recorded in natural isotopic composition in the region of 426 GHz to 785 GHz. Additional measurements were carried out near 110 GHz. Combining these with earlier data resulted in greatly improved spectroscopic parameters which permit reliable extrapolations up to about 1.5 THz. Coupled cluster quantum-chemical calculations were carried out in order to assess the differences between equilibrium and ground state rotational parameters of these and many other isotopic species to evaluate semi-empirical equilibrium structural parameters. In addition, we estimated the main spectroscopic parameters of the isotopomers of propyne with two $^{13}$C atoms, which have not yet been studied in the laboratory, but which may be detectable in astronomical sources with a large amount of $^{13}$C compared to the dominant $^{12}$C.

astro-ph.IM↗

arXiv2019

Submillimeter spectroscopy and astronomical searches of vinyl mercaptan, C$_2$H$_3$SH

We have extended the pure rotational investigation of the two isomers syn and anti vinyl mercaptan to the millimeter domain using a frequency-multiplication spectrometer. The species were produced by a radiofrequency discharge in 1,2-ethanedithiol. Additional transitions have been re-measured in the centimeter band using Fourier-transform microwave spectroscopy to better determine rest frequencies of transitions with low-$J$ and low-$K_a$ values. Experimental investigations were supported by quantum chemical calculations on the energetics of both the [C$_2$,H$_4$,S] and [C$_2$,H$_4$,O] isomeric families. Interstellar searches for both syn and anti vinyl mercaptan as well as vinyl alcohol were performed in the EMoCA (Exploring Molecular Complexity with ALMA) spectral line survey carried out toward Sagittarius (Sgr) B2(N2) with the Atacama Large Millimeter/submillimeter Array (ALMA). Highly accurate experimental frequencies (to better than 100 kHz accuracy) for both syn and anti isomers of vinyl mercaptan have been measured up to 250 GHz; these deviate considerably from predictions based on extrapolation of previous microwave measurements. Reliable frequency predictions of the astronomically most interesting millimeter-wave lines for these two species can now be derived from the best-fit spectroscopic constants. From the energetic investigations, the four lowest singlet isomers of the [C$_2$,H$_4$,S] family are calculated to be nearly isoenergetic, which makes this family a fairly unique test bed for assessing possible reaction pathways. Upper limits for the column density of syn and anti vinyl mercaptan are derived toward the extremely molecule-rich star-forming region Sgr B2(N2) enabling comparison with selected complex organic molecules.

astro-ph.GA↗

arXiv2016

Molecular Polymorphism: Microwave Spectra, Equilibrium Structures, and an Astronomical Investigation of the HNCS Isomeric Family

The rotational spectra of thioisocyanic acid (HNCS), and its three energetic isomers (HSCN, HCNS, and HSNC) have been observed at high spectral resolution by a combination of chirped-pulse and Fabry-Pérot Fourier-transform microwave spectroscopy between 6 and 40~GHz in a pulsed-jet discharge expansion. Two isomers, thiofulminic acid (HCNS) and isothiofulminic acid (HSNC), calculated here to be 35-37~kcal/mol less stable than the ground state isomer HNCS, have been detected for the first time. Precise rotational, centrifugal distortion, and nitrogen hyperfine coupling constants have been determined for the normal and rare isotopic species of both molecules; all are in good agreement with theoretical predictions obtained at the coupled cluster level of theory. On the basis of isotopic spectroscopy, precise molecular structures have been derived for all four isomers by correcting experimental rotational constants for the effects of rotation-vibration calculated theoretically. Formation and isomerization pathways have also been investigated; the high abundance of HSCN relative to ground state HNCS, and the detection of strong lines of SH using CH$_3$CN and H$_2$S, suggest that HSCN is preferentially produced by the radical-radical reaction HS + CN. A radio astronomical search for HSCN and its isomers has been undertaken toward the high-mass star-forming region Sgr B2(N) in the Galactic Center with the 100 m Green Bank Telescope. While we find clear evidence for HSCN, only a tentative detection of HNCS is proposed, and there is no indication of HCNS or HSNC at the same rms noise level. HSCN, and tentatively HNCS, displays clear deviations from a single-excitation temperature model, suggesting weak masing may be occurring in some transitions in this source.

astro-ph.GA↗

arXiv2011

Hot HCN around young massive stars at 0.1" resolution

Massive stars form deeply embedded in dense molecular gas, which they stir and heat up and ionize. During an early phase, the ionization is confined to hypercompact HII regions, and the stellar radiation is entirely absorbed by dust, giving rise to a hot molecular core. To investigate the innermost structure of such high-mass star-forming regions, we observed vibrationally excited HCN (via the direct $\ell$-type transition of v2=1, $ΔJ$=0, J=13, which lies 1400 K above ground) toward the massive hot molecular cores G10.47+0.03, SgrB2-N, and SgrB2-M with the Very Large Array (VLA) at 7 mm, reaching a resolution of about 1000 AU (0.1"). We detect the line both in emission and in absorption against HII regions. The latter allows to derive lower limits on the column densities of hot HCN, which are several times $10^{19}$ cm$^{-2}$. We see indication of expansion motions in G10.47+0.03 and detect velocity components in SgrB2-M at 50, 60, and 70 km/s relative to the Local Standard of Rest. The emission originates in regions of less than 0.1 pc diameter around the hypercompact HII regions G10.47+0.03 B1 and SgrB2-N K2, and reaches brightness temperatures of more than 200 K. Using the three-dimensional radiative transfer code RADMC-3D, we model the sources as dense dust cores heated by stars in the HII regions, and derive masses of hot (>300 K) molecular gas of more than 100 solar masses (for an HCN fractional abundance of 10$^{-5}$), challenging current simulations of massive star formation. Heating only by the stars in the HII regions is sufficient to produce such large quantities of hot molecular gas, provided that dust is optically thick to its own radiation, leading to high temperatures through diffusion of radiation.

astro-ph.GA↗

arXiv2008

Synergy of multifrequency studies from observations of NGC6334I

We combine multifrequency observations from the millimeter to near infrared wavelengths that demonstrate the spatial distributions of H2, CO, and NH3 emission, which are all manifestations of various shocks driven by outflows of deeply embedded sources in NGC6334I. In addition to the well-known northeast-southwest outflow we detect at least one more outflow in the region by combining observations from APEX, ATCA, SMA, Spitzer and VLT/ISAAC. Potential driving sources will be discussed. NGC6334I exhibits several signs of active star formation and will be a major target for future observatories such as Herschel and ALMA.

astro-ph↗