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Linear tricarbon selenide, C3Se, has been studied spectroscopically for the first time using a combination of high-resolution infrared and microwave techniques. Probing laser ablation products from carbon–selenium targets in a free jet expansion with He, initial spectroscopic detection was accomplished in the infrared at a wavelength of 5 μm in search of the ν1vibrational fundamental. Along with the band of the most abundant isotopic species C380Se found centered at about 2039 cm–1, the corresponding bands of the C382Se, C378Se, C376Se, and C377Se isotopologues were also detected. Pure rotational spectra of the five C3Se isotopologues in the 8–18 GHz frequency range were observed in a supersonic jet expansion using chirped-pulse microwave spectroscopy of the discharge products of selenophene, c-C4H4Se. Spectroscopic analyses were guided by results from high-level quantum-chemical calculations carried out at the coupled-cluster level of theory using large correlation-consistent basis sets. Using the experimentally derived ground-state rotational constants of five isotopologues and calculated zero-point vibrational corrections, an accurate semiexperimental equilibrium carbon–selenium bond length is derived.

We present the first observation of vibrational transitions in the [H3O]−anion, an intermediate in the anion–molecule reaction of water, H2O, and hydride, H–, using a laser-induced isotopic H/D exchange reaction action spectroscopy scheme applied to anions. The observed bands are assigned as the fundamental and first overtone of the H2O–H–vibrational stretching mode, based on anharmonic calculations within the vibrational perturbation theory and vibrational configuration interaction. Although the D2O·D–species has the lowest energy, our experiments confirm the D2O·H–isotope to be a sink of the H/D exchange reaction. Ab initiocalculations corroborate that the formation of D2O·H–is favored, as the zero-point-energy difference is larger between D2and H2than between D2O·H–and D2O·D–.

Forty years ago, it was proposed that gas-phase organic chemistry in the interstellar medium can be initiated by the methyl cation CH3+(refs. 1–3), but so far it has not been observed outside the Solar System4,5. Alternative routes involving processes on grain surfaces have been invoked6,7. Here we report James Webb Space Telescope observations of CH3+in a protoplanetary disk in the Orion star-forming region. We find that gas-phase organic chemistry is activated by ultraviolet irradiation.

Sulfoxylic acid (HOSOH), a chemical intermediate roughly midway along the path between highly reduced (H2S) and highly oxidized sulfur (H2SO4), has been detected using Fourier transform microwave spectroscopy and double resonance techniques, guided by new high-level CCSD(T) quantum-chemical calculations of its molecular structure. Rotational spectra of the two most stable isomers of HOSOH, the putative ground state with C2symmetry and the low-lying Csrotamer, have been measured to high precision up to 71 GHz, allowing accurate spectroscopic parameters to be derived for both isomers. HOSOH may play a role in atmospheric and interstellar chemistry, and the present work provides the essential data to enable remote sensing and/or radioastronomical searches for these species. Spectroscopic characterization of HOSOH suggests that other transient intermediates in the oxidation of SO2to H2SO4may be amenable to laboratory detection as well.

The rotational spectrum of nitrogen-protonated nitrous oxide (\ce{HNNO+}), an isomer whose existence was first inferred from kinetic studies more than 30 years ago, has now been detected by Fourier transform microwave spectroscopy, guided by new high-level coupled-cluster calculations of its molecular structure. From high-resolution measurements of the hyperfine splitting in its fundamental rotational transition, the rotational constant ($B+C$)/2 and the quadrupole tensor element $\chi_{aa}$(N) for both nitrogen atoms have been precisely determined. The derived constants agree well with quantum-chemical calculations here and others in the literature. The $\chi_{aa}$(N) values for the two isomers of protonated nitrous oxide are qualitatively consistent with the valence bond description of \ce{H\bond{-}N\bond{=}N+\bond{=}O} for the electronic structure of the nitrogen-protonated form and \ce{N\bond{#}N+\bond{-}O\bond{-}H} for the oxygen-protonated form. \ce{HNNO+} is found to be 2-4 times less abundant than \ce{NNOH+} under a range of experimental conditions, as might be expected because this metastable isomer is known to be only $\sim$6~kcal mol$^{-1}$ less stable than ground state \ce{NNOH+} from kinetic measurements by Ferguson and co-workers.

We report on the detection of the (1001) ← (0000) vibrational band of gas-phase C3and the two of its mono 13C substituted isotopologs in the infrared region around 3200 cm–1. Additionally, the associated hot band (1111) ← (0110) has been assigned for the parent isotopolog. Spectra have been recorded using a supersonic jet spectrometer with a laser ablation source in combination with a continuous-wave optical parametric oscillator as radiation source. High-level quantum-chemical ab initio calculations have been performed and used to assist the assignment. A combined fit for the vibrational states of C3found in this study has been done together with previously reported high-resolution data to increase the accuracy of the molecular parameters, especially for the ground state. The vibrational energies are 3260.126, 3205.593, and 3224.751 cm–1for the (1001) state of C3, 12C13C12C, and 13C12C12C, respectively. The (1111) state of C3has been found to be at 3330.509 cm–1.

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 three 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.

A joint effort: By means of high‐resolution rotational spectroscopy and highly accurate quantum‐chemical calculations, the first observation and characterization of cyclic SiS2was achieved. This provides a new perspective on the Walsh rules: Although the cyclic form of SiS2is a local and not the global minimum, cyclic isomers of sixteen‐electron triatomics containing second or even higher row elements are experimentally accessible.

Lokal stabil: Durch die Kombination von hochauflösender Rotationsspektroskopie mit quantenchemischen Rechnungen konnte zum ersten Mal cyclisches SiS2nachgewiesen und charakterisiert werden. Die Walsh‐Regeln erscheinen so in neuem Licht: Obwohl die cyclische Form von SiS2nur ein lokales Minimum ist, sind cyclische Isomere von dreiatomigen Spezies mit 16 Valenzelektronen experimentell zugänglich, sofern sie Elemente der dritten oder höherer Perioden enthalten.

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Brücken schlagen: Durch Kombination von hochauflösender Molekülspektroskopie im cm‐ und mm‐Wellenbereich mit quantenchemischen Coupled‐Cluster‐Rechnungen auf hohem Theorieniveau wurde die Struktur von HPSi ermittelt. Seine verbrückte Struktur (siehe Bild; berechnete Werte in Klammern) unterscheidet sich in bemerkenswerter Weise von den linearen Strukturen der C‐ und N‐Analoga wie HCN/HNC und HNSi.

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 ν1of linear C3H+. Besides performing high-resolution spectroscopy, this method opens up the way for analyzing the composition of trap content, for example, 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.

The pure rotational spectra of phenanthridine, acridine, and 1,10-phenanthroline, small polycyclic aromatic nitrogen heterocycle molecules (PANHs), have been measured and assigned from 2 to 85 GHz. An initial spectral assignment, guided by ab initio molecular orbital predictions, employed broadband Stark modulated millimeter wave absorption spectroscopy of a supersonic rotationally cold molecular beam, yielding a preliminary set of rotational and centrifugal distortion constants. Subsequent spectral analysis employed Fourier transform microwave (FT-MW) spectroscopy of a supersonic rotationally cold molecular beam. The extremely high spectral resolution of the FT-MW instrument yielded improved rotational constants and centrifugal distortion constants, together with nitrogen quadrupole coupling constants, for all three species. Density functional theory (DFT) calculations at the B3LYP level of theory employing the cc-pVTZ and 6-311+G** basis sets are shown to closely predict rotational constants and to be useful in predicting quadrupole coupling constants and dipole moments for such PANH species. The data presented here will be useful for deep radio astronomical searches for PANHs employing large radio telescopes.

Gas‐phase oxadisulfane (HSOH), the missing link between the well‐known molecules hydrogen peroxide (HOOH) and disulfane (HSSH), was synthesized by flash vacuum pyrolysis of di‐tert‐butyl sulfoxide. Using mass spectrometry, the pyrolysis conditions have been optimized towards formation of HSOH. Microwave spectroscopic investigation of the pyrolysis products allowed—assisted by high‐level quantum‐chemical calculations—the first measurement of the rotational‐torsional spectrum of HSOH. In total, we have measured approximately 600 lines of the rotational‐torsional spectrum in the frequency range from 64 GHz to 1.9 THz and assigned some 470 of these to the rotational‐torsional spectrum of HSOH in its ground torsional state. Some 120 out of the 600 lines arise from the isotopomer H34SOH. The HSOH molecule displays strong c‐type and somewhat weaker b‐type transitions, indicating a nonplanar skew chain structure, similar to the analogous molecules HOOH and HSSH. The rotational constants (MHz) of the main isotopomer (A=202 069, B=15 282, C=14 840), determined by applying a least‐squares analysis to the presently available data set, are in excellent agreement with those predicted by quantum‐chemical calculations (A=202 136, B=15 279, C=14 840). Our theoretical treatment also derived the following barrier heights against internal rotation in HSOH (when in the cisand transconfigurations) to be Vcis≈2216 cm−1and Vtrans≈1579 cm−1. The internal rotational motion results in detectable torsional splittings that are dependent on the angular momentum quantum numbers Jand Ka.

Gas-phase oxadisulfane (HSOH), the missing link between the well-known molecules hydrogen peroxide (HOOH) and disulfane (HSSH), was synthesized by flash vacuum pyrolysis of di-tert-butyl sulfoxide. Using mass spectrometry, the pyrolysis conditions have been optimized towards formation of HSOH. Microwave spectroscopic investigation of the pyrolysis products allowed—assisted by high-level quantum-chemical calculations—the first measurement of the rotational-torsional spectrum of HSOH. In total, we have measured approximately 600 lines of the rotational-torsional spectrum in the frequency range from 64 GHz to 1.9 THz and assigned some 470 of these to the rotational-torsional spectrum of HSOH in its ground torsional state. Some 120 out of the 600 lines arise from the isotopomer H³⁴SOH. The HSOH molecule displays strong c-type and somewhat weaker b-type transitions, indicating a nonplanar skew chain structure, similar to the analogous molecules HOOH and HSSH. The rotational constants (MHz) of the main isotopomer (A=202 069, B=15 282, C=14 840), determined by applying a least-squares analysis to the presently available data set, are in excellent agreement with those predicted by quantum-chemical calculations (A=202 136, B=15 279, C=14 840). Our theoretical treatment also derived the following barrier heights against internal rotation in HSOH (when in the cis and trans configurations) to be Vcis≈2216 cm⁻¹ and Vtrans≈1579 cm⁻¹. The internal rotational motion results in detectable torsional splittings that are dependent on the angular momentum quantum numbers J and Ka.

The submillimeter-wave rotational spectra of the unstable phosphorus-bearing molecules HCCCP (phosphabutadiyne) and NCCP (C-cyanophosphaethyne) have been investigated in selected frequency regions between 490 and 815 GHz using the Cologne Terahertz Spectrometer. Both molecules were studied in their ground vibrational states. Additionally, vibrational satellites within the bending states v4= 1 and v5= 1 were recorded for NCCP. Furthermore, the ground state rotational spectra of the 13C and 15N isotopomers of NCCP were detected in natural abundance. The new measurements allowed us to evaluate the sextic centrifugal distortion constants for each isotopomer and vibrational state investigated. The pyrolysis reactions, through which HCCCP and NCCP were produced in situ,also yielded phosphaethyne, HCP, as a by-product. Some transitions of HCP and DCP were recorded in their ground vibrational states along with v2= 1 vibrational satellites of the former.

The ground state rotational spectrum of propyne has been studied in selected regions between 509 and 820 GHz spanning the quantum numbers 29

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