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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–.

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.