Search

Detecting anions in space has relied on a strong collaboration between theoretical and laboratory analyses to measure rotational spectra and spectroscopic constants to high accuracy. The advent of improved quantum chemical tools operating at higher accuracy and reduced computational cost is a crucial solution for the fundamental characterization of astrophysically relevant anions and their detection in the interstellar medium (ISM) and planetary atmospheres. In this context, we have turned toward the quantum chemical analysis of the penta-atomic dicyanoamine anion NCNCN− (), a structurally bent and polar compound. We have performed high-level coupled cluster theory quartic force field computations of satisfying both computational cost and accuracy conditions. We provide for the first time accurate spectroscopic constants and vibrational frequencies for this ion. In addition to exhibiting various Fermi resonances, displays a bright ν2 (2130.9 cm−1) and a less intense ν1 (2190.7 cm−1) fundamental vibrational frequency, making for strong markers for future infrared observations <5 μm. We have also determined near-IR overtone and combination bands of the bright fundamentals for which the 2ν2 at 4312.1 cm−1 (2.319 μm) is the best candidate. could potentially exist and be detected in nitrogen-rich environments of the ISM such as IRC +10216 and other carbon-rich circumstellar envelopes, or in the atmosphere of Saturn’s moon Titan, where advanced N-based reactions may lead to its formation. [ABSTRACT FROM AUTHOR]

Methoxymethanol (CH3OCH2OH) was recently detected toward the MM1 core in the high-mass star-forming region NGC 6334I. However, the underlying formation mechanisms of this complex organic molecule (COM) as well as its structural isomers ethylene glycol (HOCH2CH2OH) and the hitherto unobserved dimethyl peroxide (CH3OOCH3) are still elusive. Here, we report the very first confirmed synthesis of dimethyl peroxide—at various deuteration levels within interstellar analogous ices of D3-methanol (CD3OH) exposed to ionizing radiation at ultralow temperatures of 5 K. The discrimination of specific isomers is achieved by exploiting reflectron time-of-flight mass spectrometry coupled with isomer-selective photoionization of the subliming molecules in the temperature programmed desorption phase of the experiment. Based on the distribution of the identified species at distinct mass-to-charge ratios, we reveal primary and secondary reaction pathways to methoxymethanol, ethylene glycol, and dimethyl peroxide involving radical–radical recombination of methoxy (CH3O) and hydroxymethyl (CH2OH). Our findings help to constrain the formation mechanism of COMs detected within star-forming regions (methoxymethanol, ethylene glycol) and propose that the hitherto elusive dimethyl peroxide isomer represents an excellent candidate for future astronomical searches. [ABSTRACT FROM AUTHOR]

The cyclopropenylidenyl carbene, c-(C)C3H2, should make for an excellent probe of unidentified infrared bands. It has a dipole moment of roughly 5.0 D making it easily detectable rotationally from the ground. Furthermore, it has vibrational frequencies computed here with proven and high-level quantum chemical methods that line up rather well with the typical C−H stretch, C−C stretch, out-of-plane wag, etc., bins delineated for polycyclic aromatic hydrocarbon fundamental frequencies. For instance, the bright C = C stretches are predicted to be at 5.474 and 6.394 μm, in line with the aromatic infrared bands observed toward various astrophysical regions and within the range of the EXES instrument on board the Stratospheric Observatory for Infrared Astronomy. As a result, potential radioastronomical detection of this molecule could be followed with IR analysis leading to a rare two-pronged analysis for this hydrocarbon, which should shed light onto the nature of currently unattributed IR features. [ABSTRACT FROM AUTHOR]

S2H (HSS) has been observed very recently in the interstellar medium, specifically in the Horsehead nebula. The protonated form, S2H2+, is believed to be a necessary intermediate in its creation in the gas phase in UV-irradiated regions. However, little is known about this radical cation. This work showcases that the trans-HSSH+ isomer is 0.12 eV lower in energy than the cis with a 1.05 eV upper limit to the torsional rotation barrier. Additionally, the vibrational frequencies and rotational constants for both structures are provided in full here for the first time. The cis isomer is likely the more detectable since it possesses a permanent dipole moment and has a high-intensity vibrational frequency for the antisymmetric H−S−S bend at 926 cm−1 (10.8 μm), in the heart of the mid-IR spectral range. A third isomer, H2S−S+ is also reported herein lying ∼0.9 eV in energy above trans-HSSH+. This isomer could play a role in the formation of S2H since it would be kinetically favored in the reaction of sulfur cations with hydrogen sulfide. Further assessment of this third, higher-energy isomer is left for future work. [ABSTRACT FROM AUTHOR]

The SiP radical has a ground state and a low-lying state with a transition wavelength of greater than 20 μm. However, this transition has a near-zero oscillator strength making it all but unobservable. Addition of a hydrogen atom to the system creates the strangely bent HPSi molecule and also the linear HSiP isomer, lying 0.50 eV above the bent. The electron-deficient P–Si π cloud in SiP is stabilized by the addition of the hydrogen atom, making this isomer the preferred form of HPSi. The HSiP linear isomer can be formed from SiP. As a result, the [HPSi]/[HSiP] ratio could serve as tracer of the otherwise unobservable but low-lying electronic transition of SiP. The high-level quantum chemical computations employed here imply that the rotational lines of HPSi and HSiP will overlap extensively, but the vibrational frequencies, especially the hydride stretch, are significantly separated. The hydride stretches are in the 5 μm range, making them excellent candidates for mid-IR observations with the Stratsopheric Observatory for Infrared Astronomy or with the James Webb Space Telescope. Furthermore, the rotational constants and vibrational frequencies of SiP, SiP, and SiP− are also provided in addition to the relative energies of all five species. [ABSTRACT FROM AUTHOR]

HSS has yet to be observed in the gas phase in the interstellar medium (ISM). HSS has been observed in cometary material and in high abundance. However, its agglomeration to such bodies or dispersal from them has not been observed. Similarly, HSO and HOS have not been observed in the ISM, either, even though models support their formation from reactions of known sulfur monoxide and hydrogen molecules, among other pathways. Consequently, this work provides high-level, quantum chemical rovibrational spectroscopic constants and vibrational frequencies in order to assist in interstellar searches for these radical molecules. Furthermore, the HSO−HOS isomerization energy is determined to be 3.63 kcal mol−1, in line with previous work, and the dipole moment of HOS is 36% larger at 3.87 D than HSO, making the less stable isomer more rotationally intense. Finally, the S−S bond strength in HSS is shown to be relatively weak at 30% of the typical disulfide bond energy. Consequently, HSS may degrade into SH and sulfur atoms, making any ISM abundance of HSS likely fairly low, as recent interstellar surveys have observed. [ABSTRACT FROM AUTHOR]

Proton-bound complexes have been hypothesized as further means of detecting the nitrogen molecule in the interstellar medium. The study of such complexes has largely been hindered by the necessary experimental setups utilized or by their difficulty in producing and/or analyzing computed potential energy surfaces. Here the NN–HCO+ proton-bound complex is analyzed via quartic force fields (QFFs). While QFFs have produced meaningful results for other proton-bound complexes, they have been hindered by double-well potentials or flat potential surfaces. NN–HCO+ is not affected by these constraints. This strongly dipolar (3.63 D) molecule can be observed rotationally unlike the more heavily analyzed OCHCO+ and NNHNN+ proton-bound complexes. Additionally, the large absorption feature corresponding to the proton motion, a hallmark of proton-bound complexes, is much higher in frequency at 2547.1 cm−1, changing the range of experimental observation for the bright frequency. NN–HCO+ is hypothesized to be present in protoplanetary disks where N2H+ and CO are known. As such, it may help to influence the nitrogen budget of planet-forming astronomical regions. [ABSTRACT FROM AUTHOR]