•We report the first infrared emission measurements of ball plasmoid discharges.•The details of fitting the rotationally-resolved spectra using the PGOPHER software are also presented.•Temperatures of the bending and stretching modes of water are found to be 1900 ± 300 K and 2400 ± 400 K.•The rotational temperature of OH was found to be 9200 ± 1500 K.We report the first (to our knowledge) infrared emission spectra collected from water-based laboratory ball plasmoid discharges. A “ball plasmoid” results from a unique type of pulsed DC plasma discharge in which a sphere of plasma is seen to grow and eventually separate from a central electrode and last for a few hundred milliseconds without an external power source before dissipating. Typical recombination rates for plasmas at ambient conditions are on the order of a millisecond or less, however ball plasmoids have been observed to last a few hundred milliseconds, and there is no explanation in the literature that fully accounts for this large discrepancy in lifetime. The spectra are dominated by emission from water and from hydroxyl radical; PGOPHER was used to fit the experimental spectra to extract rotational temperatures for these molecules. The temperatures of the bending and stretching modes of H2O were determined to be 1900 ± 300 K and 2400 ± 400 K, respectively and the rotational temperature of OH was found to be 9200 ± 1500 K.

Ball lightning is a naturally occurring atmospheric event that has perplexed researchers for centuries, and there is to date no complete explanation (chemical, physical, or otherwise) as to why ball lightning behaves the way that it does. There has been considerable effort to try to both produce and measure the properties of ball lightning type discharges over recent years, and this collected work has begun to reveal some interesting physical and chemical phenomena. We are able to produce water-based plasma ball discharges using high-voltage equipment, and these self-contained plasmoids are considered to be similar to natural ball lightning. In this article we present the first mass spectrometric analysis of water-based ambient ball plasmoids. Using an extremely simple sampling technique, we were able to detect several chemical species within the interior of the plasmoid. Several molecules that are common to plasmas generated in air were observed in the mass spectra, such as [NO2]+ and [NO3]+. More interestingly, we observed the protonated water clusters [(H2O)2H]+ and [(H2O)3H]+, ammonia (NH3) as a component of a copper cluster, and several anions. Furthermore, many species observed in the mass spectra are in the form of hydrated clusters.

•We observed ν16ν16 absorption band of 1,3,5-trioxane using cavity ringdown spectroscopy.•219 transitions were assigned and fitted to a simulated spectrum.•New excited state rotational constants have been determined.Rotationally-resolved spectra of the ν16ν16 band of 1,3,5-trioxane, centered near 1177 cm-1cm-1, have been obtained via cavity ringdown spectroscopy using a continuous-wave external-cavity quantum cascade laser and a slit expansion nozzle. 219 transitions were identified and fitted to determine the excited state rotational constants for this band. In addition to fundamental interest, these data could facilitate spectroscopic detection of trioxane in cometary comae as a tracer for polyoxymethylene.

High-resolution spectra of the intramolecular bending modes of deuterated water dimer, (D2O)2, have been measured using a quantum cascade laser based cavity ringdown spectrometer. Two perpendicular bands have been observed and are assigned as the Ka = 1 ← 0 and Ka = 2 ← 1 bands of the bending mode of the hydrogen bond donor. The tunneling splittings in the complex are well-resolved, and it is found that excitation of the donor bend has little effect on tunneling of the hydrogen bond acceptor, but causes significant perturbations on the tunneling motion which exchanges the roles of hydrogen bond donor and acceptor. The presence of this perturbation has prevented a detailed assignment of the tunneling levels in the excited state at this time. An accurate value for the band center of the donor bend is calculated to be 1182.2 cm–1, which is in good agreement with previous theoretical calculations performed on an ab initio potential energy surface.

Spectroscopy of the ν1 band of the astrophysically relevant ion HCO+ is performed with an optical parametric oscillator calibrated with an optical frequency comb. The sub-MHz accuracy of this technique was confirmed by performing a combination differences analysis with the acquired rovibrational data and comparing the results to known ground-state rotational transitions. A similar combination differences analysis was performed from the same data set to calculate the previously unobserved rotational spectrum of the ν1 vibrationally excited state with precision sufficient for astronomical detection. Initial results of cavity-enhanced sub-Doppler spectroscopy are also presented and hold promise for further improving the accuracy and precision in the near future.

The fundamental molecular ion H3+ has impacted astronomy, chemistry, and physics, particularly since the discovery of its rovibrational spectrum. Consisting of three identical fermions, its properties are profoundly influenced by the requirements of exchange symmetry, most notably the nonexistence of its ground rotational state. Spectroscopy of H3+ is often used to infer the relative abundances of its two nuclear spin modifications, ortho- and para-H3+, which are important in areas as diverse as electron dissociative recombination and deuterium fractionation in cold interstellar clouds. In this paper, we explore in detail the impact of exchange symmetry on the states of H3+, with a particular focus on the state degeneracies necessary for converting spectral transition intensities to relative abundances. We address points of confusion in the literature surrounding these issues and discuss the implications for proton-transfer reactions of H3+ at low temperatures.

Three new rovibrational bands of Ar–D2O have been observed in the ν2 bending region of D2O using a quantum cascade laser based cavity ringdown spectrometer. In addition, further observations of the Π(110, ν2 = 1) ← Σ(101) band reported by Li et al. (J. Mol. Spectrosc. 272 (2012) 27–31) have been made. All bands were fit by treating the complex using a pseudo-diatomic model which treats the D2O as a free rotor within the complex. Molecular constants have been obtained using this model and are reported with deviations in the fits ranging from 0.0002 cm−1 to 0.0005 cm−1. Two of the newly observed bands are tentatively assigned as the Π(202, ν2 = 1) ← Σ(111) and Π(211, ν2 = 1) ← Σ(202) bands, which have not previously been observed in other spectral regions.Graphical abstractHighlights► Measured three new rovibrational bands of Ar–D2O in the ν2 bending region of D2O. ► Measured additional transitions of the strongest band of para Ar–D2O. ► Fit each band using a pseudo-diatomic model to obtain accurate molecular constants.

The technique of velocity modulation spectroscopy has recently been combined with cavity enhancement and frequency modulation methods into a technique called noise-immune cavity-enhanced optical heterodyne velocity modulation spectroscopy (NICE-OHVMS). We have implemented NICE-OHVMS with a cw-optical parametric oscillator (OPO) tunable from 3.2 to 3.9 μm, and used it to record spectra of the R(1,0) and R(1,1)u transitions of the ν2ν2 fundamental band of H3+. The high optical power and cavity enhancement enable saturation of rovibrational transitions, which allows for line center frequencies to be measured with a precision of 70 kHz.Graphical abstractHighlights► An instrument for sub-Doppler mid-IR spectroscopy of molecular ions is described. ► NICE-OHMS is performed with an optical parametric oscillator (OPO). ► Fitting to Lamb dips provides ∼70 kHz precision in line center determination. ► Velocity modulation with phase sensitive detection gives ion-neutral discrimination. ► A sensitivity of 8.5×10-10cm-1Hz-1/2 is achieved.

We report the rotationally resolved gas phase spectrum of pyrene (C16H10), which is now the largest molecule to be observed with rotational resolution using absorption spectroscopy. This represents a significant advance in the application of absorption spectroscopy to large carbon-containing molecules of fundamental chemical and astronomical importance. Such spectra will facilitate the search for large and highly symmetric molecules in interstellar space, where they may be abundant but cannot be detected without the support of high-resolution laboratory spectra. Detailed assignment and analysis of our spectrum indicates that pyrene is the most rigid rotor yet observed, and that a supersonic expansion cools both the rotational and vibrational temperatures of pyrene vapor produced in an oven source.Keywords: polycylic aromatic hydrocarbon; quantum cascade laser; rigid rotor;

A continuous wave cavity ringdown spectrometer with a Fabry-Perot quantum cascade laser has been used to collect a rotationally-resolved infrared spectrum of the ν8 vibrational band of methylene bromide in a slit nozzle expansion. In our laboratory, previous observations of the vibrational band were limited by spectral coverage to only the P and Q-branches and by the 24 MHz step-size of the laser [1]. The issue of limited spectral coverage has been resolved using a Fresnel rhomb and a wire grid polarizer to protect the laser from the destabilizing effects of back-reflection from the ringdown cavity. The frequency step-size of the spectrometer has been reduced from 24 MHz to 2 MHz. With both of these instrument enhancements, we have been able to record the R-branch of the vibrational band, and can resolve many lines that were previously blended in spectra acquired using a pinhole expansion nozzle. Significant hyperfine splitting was observed for the low-J transitions in the P and R-branches. It was possible to neglect the effects of hyperfine splitting for transitions involving J″ > 2 in the spectral assignment, and simulations using the constants obtained by fitting to Watson’s S-reduced Hamiltonian for CH279Br81Br, and the A-reduced form for CH279Br2 and CH281Br2, provide a good match to experimental spectra. A total of 297 transitions have been assigned for all three isotopologues, with a standard deviation of 0.00024 cm−1(∼7 MHz).Graphical abstract■■■Research Highlights► Rotationally resolved spectrum of the ν8 band of methylene bromide was collected. ► A total of 297 transitions were assigned in the vibrational band. ► Fitting of vibrational band yielded excited state rotational constants. ► Substantial hyperfine splitting observed for low-J transitions.

Nuclear permutation-inversion (PI) group theory and the linear combination of localized wavefunctions (LCLW) method are applied to the proton “ring-walk” tunneling problem in C6D6H+ and the benzenium ion (C6H7+). For C6D6H+ and C6H7+, the rigid and non-rigid MS groups are developed, and their corresponding correlation tables constructed. The reverse correlation relationship is combined with spin statistical restrictions to determine the number of allowed tunneling split levels for both ions. Through the use of the LCLW method and the WKB approximation, the qualitative pattern of the tunneling splitting is presented for C6D6H+. Application of the LCLW problem for the benzenium ion is presented, but the complete treatment to obtain the structure of the tunneling split levels is limited by the computational expense of obtaining the eigenvectors from the diagonalization of the 15 120 × 15 120 connectivity matrix.Graphical abstractThe graphical abstract illustrates the permutation operation corresponding to the proton “ring-walk” pathway in the non-rigid benzenium ion.Highlights► Permutation inversion group theory is applied to benzenium ion and C6D6H+. ► The proton ring-walk tunneling pathway is treated in group theoretical analysis. ► WKB approximation and LCLW method determine qualitative tunneling splitting in C6D6H+. ► Benzenium ion ground state rotational levels shown to split 16–19 times. ► The rotational level splitting is estimated to span 48 MHz.