A local mode study of ring puckering effects in the infrared spectra of cyclopentane.

We report and interpret recently recorded high-resolution infrared spectra for the fundamentals of the CH scissors and CH stretches of gas phase cyclopentane at -26.1 and -50 °C, respectively. We extend previous theoretical studies of this molecule, which is known to undergo barrierless pseudorotation due to ring puckering, by constructing local mode Hamiltonians of the stretching and scissor vibrations for which the frequencies, couplings, and linear dipoles are calculated as functions of the pseudorotation angle using B3LYP/6-311++(d,p) and MP2/cc-pVTZ levels of theory.

Wildfire smoke destroys stratospheric ozone.

Large wildfires inject smoke and biomass-burning products into the mid-latitude stratosphere, where they destroy ozone, which protects us from ultraviolet radiation. The infrared spectrometer on the Atmospheric Chemistry Experiment satellite measured the spectra of smoke particles from the "Black Summer" fires in Australia in late 2019 and early 2020, revealing that they contain oxygenated organic functional groups and water adsorption on the surfaces. These injected smoke particles have produced unexpected and extreme perturbations in stratospheric gases beyond any seen in the previous 15 years of measurements, including increases in formaldehyde, chlorine nitrate, chlorine monoxide, and hypochlorous acid and decreases in ozone, nitrogen dioxide, and hydrochloric acid.

Cyclohexane Vibrations: High-Resolution Spectra and Anharmonic Local Mode Calculations.

High-resolution infrared absorption spectra of cyclohexane have been recorded from 1100 to 4000 cm at room temperature and 241 K. Cyclohexane is an oblate symmetric top with symmetry. A rotational analysis was obtained for the ν (e) and ν (a) CH scissor modes at 1452.

Neopentane Vibrations: High Resolution Spectra and Anharmonic Calculations.

High resolution infrared absorption spectra of neopentane (2,2-dimethylpropane, CH) have been recorded in the mid-infrared region at room temperature and 232 K. Neopentane is a spherical top with symmetry. The high symmetry and low temperature allow for detailed comparison of theory and experiment for the analysis of the fundamental vibrations.

Isobutane Infrared Bands: Partial Rotational Assignments, ab Initio Calculations, and Local Mode Analysis.

High-resolution infrared spectra of the symmetric top isobutane CH(CH) were assigned with the help of ab initio calculations. The strong parallel band ν(a) with an origin at 1396.54741(76) cm and the ν(a) mode, the CH scissors, at 1478.

Recent Trends in Stratospheric Chlorine From Very Short-Lived Substances.

Very short-lived substances (VSLS), including dichloromethane (CHCl), chloroform (CHCl), perchloroethylene (CCl), and 1,2-dichloroethane (CHCl), are a stratospheric chlorine source and therefore contribute to ozone depletion. We quantify stratospheric chlorine trends from these VSLS (VSLCl) using a chemical transport model and atmospheric measurements, including novel high-altitude aircraft data from the NASA VIRGAS (2015) and POSIDON (2016) missions. We estimate VSLCl increased from 69 (±14) parts per trillion (ppt) Cl in 2000 to 111 (±22) ppt Cl in 2017, with >80% delivered to the stratosphere through source gas injection, and the remainder from product gases.

Study of infrared emission spectroscopy for the B(1)Δg-A(1)Πu and B'(1)Σg(+)-A(1)Πu systems of C2.

Thirteen bands for the B(1)Δg-A(1)Πu system and eleven bands for the B'(1)Σg(+)-A(1)Πu system of C2 were identified in the Fourier transform infrared emission spectra of hydrocarbon discharges. The B'(1)Σg(+)v = 4 and the B(1)Δg v = 6, 7, and 8 vibrational levels involved in nine bands were studied for the first time. A direct global analysis with Dunham parameters was carried out satisfactorily for the B(1)Δg-A(1)Πu system except for a small perturbation in the B(1)Δg v = 6 level.

Note: Improved line strengths of rovibrational and rotational transitions within the X(3)Σ(-) ground state of NH.

Recently, a line list including positions and transition strengths was published for the NH X(3)Σ(-) rovibrational and rotational transitions. The calculation of the transition strengths requires a conversion of transition matrix elements from Hund's case (b) to (a). The method of this conversion has recently been improved during other work on the OH X(2)Π rovibrational transitions, by removing an approximation that was present previously.

Simultaneous analysis of the Ballik-Ramsay and Phillips systems of C2 and observation of forbidden transitions between singlet and triplet states.

6229 lines of the Ballik-Ramsay system (b(3)Σg (-)-a(3)Πu) and the Phillips system (A(1)Πu-X(1)Σg (+)) of C2 up to v = 8 and J = 76, which were taken from the literature or assigned in the present work, were analyzed simultaneously by least-squares fitting with 82 Dunham-like molecular parameters and spin-orbit interaction constants between the b(3)Σg (-) and X(1)Σg (+) states with a standard deviation of 0.0037 cm(-1) for the whole data set. As a result of the deperturbation analysis, the spin-orbit interaction constant AbX was determined as 6.

Relationship between dipole moments and harmonic vibrational frequencies in diatomic molecules.

Electric dipole moments and harmonic vibrational frequencies are two of the most important molecular properties in many fields of chemistry and physics. With the aid of classical physics, an empirical relationship between them was obtained for diatomic molecules as μd = kq(2)/(ReμAωe(2))(1/2), where k is a constant and μd, q, Re, μA, and ωe are the dipole moment, atomic charge, equilibrium bond length, reduced mass, and equilibrium vibrational frequency, respectively. This relation also provides the atomic charge q as a function of molecular dipole moment.

Relationships between dipole moments of diatomic molecules.

The dipole moment is one of the most important physical properties of a molecule. We present a combination rule for the dipole moments of related diatomic molecules. For molecules AB, AX, BY, and XY from two different element groups in the periodic table, if their elements make a small parallelogram, reliable predictions can be obtained.

Line strengths of rovibrational and rotational transitions within the X³Σ⁻ ground state of NH.

A new line list for rovibrational and rotational transitions, including fine structure, within the NH X³Σ⁻ ground state has been created. It contains line intensities in the form of Einstein A and f-values, for all possible bands up to v' = 6, and for J up to between 25 and 44. The intensities are based on a new dipole moment function (DMF), which has been calculated using the internally contracted multi-reference configuration interaction method with an aug-cc-pV6Z basis set.

Molecular opacities for exoplanets.

Spectroscopic observations of exoplanets are now possible by transit methods and direct emission. Spectroscopic requirements for exoplanets are reviewed based on existing measurements and model predictions for hot Jupiters and super-Earths. Molecular opacities needed to simulate astronomical observations can be obtained from laboratory measurements, ab initio calculations or a combination of the two approaches.

Accurate analytic potential and Born-Oppenheimer breakdown functions for MgH and MgD from a direct-potential-fit data analysis.

New high-resolution visible Fourier transform emission spectra of the A (2)Π → X (2)Σ(+) and B' (2)Σ(+) → X (2)Σ(+) systems of (24)MgD and of the B' (2)Σ(+) → X (2)Σ(+) systems of (25,26)MgD and (25,26)MgH have been combined with earlier results for (24)MgH in a multi-isotopologue direct-potential-fit analysis to yield improved analytic potential energy and Born-Oppenheimer breakdown functions for the ground X (2)Σ(+) state of MgH. Vibrational levels of the ground state of (24)MgD were observed up to v" = 15, which is bound by only 30.6 ± 0.

Empirical correction of thermal responses in the Solar Occultation for Ice Experiment nitric oxide measurements and initial data validation results.

The Solar Occultation for Ice Experiment (SOFIE) makes broadband transmission measurements centered at 5.32 μm to determine the concentration profile of nitric oxide (NO). These measurements show a signal oscillation due to detector temperature variations that severely limit the accuracy of NO retrievals if corrections are not applied.

Rotational analysis and deperturbation of the A2Π → X2Σ+ and B'2Σ+ → X2Σ+ emission spectra of MgH.

Deperturbation analysis of the A(2)Π → X(2)Σ(+) and B(')(2)Σ(+) → X(2)Σ(+) emission spectra of (24)MgH is reported. Spectroscopic data for the v = 0 to 3 levels of the A (2)Π state and the v = 0 to 4 levels of the B'(2)Σ(+) state were fitted together using a single Hamiltonian matrix that includes (2)Π and (2)Σ(+) matrix elements, as well as off-diagonal elements coupling several vibrational levels of the two states. A Dunham-type fit was performed and the resulting Y(l,0) and Y(l,1) coefficients were used to generate Rydberg-Klein-Rees (RKR) potential curves for the A (2)Π and the B'(2)Σ(+) states.

Note: Deperturbation of the ν3 band of BeD2.

High rotational levels of the 001 (Σ(u)) state of BeD(2) are perturbed by the nearby 03(3)0 (Φ(u)) state. Deperturbation analysis results in an experimental value for the vibrational energy of the 030 level.

Asian monsoon transport of pollution to the stratosphere.

Transport of air from the troposphere to the stratosphere occurs primarily in the tropics, associated with the ascending branch of the Brewer-Dobson circulation. Here, we identify the transport of air masses from the surface, through the Asian monsoon, and deep into the stratosphere, using satellite observations of hydrogen cyanide (HCN), a tropospheric pollutant produced in biomass burning. A key factor in this identification is that HCN has a strong sink from contact with the ocean; much of the air in the tropical upper troposphere is relatively depleted in HCN, and hence, broad tropical upwelling cannot be the main source for the stratosphere.

Optical-optical double resonance spectroscopy of the C(2)Pi-A(2)Pi and D(2)Sigma(+)-A(2)Pi transitions of SrF.

Optical-optical double resonance spectroscopy has been used to record rotationally resolved spectra of the C(2)Pi-A(2)Pi and D(2)Sigma(+)-A(2)Pi transitions of SrF. In the investigation, the spectrum of a previously unobserved (2)Sigma(+)-A(2)Pi transition was recorded. The new (2)Sigma(+) state was found to lie lower in energy than the previously labeled D(2)Sigma(+) (v = 0) state by an amount equal to the vibrational spacing of the D(2)Sigma(+) state.

Ground state potential energy curve and dissociation energy of MgH.

New high-resolution visible emission spectra of the MgH molecule have been recorded with high signal-to-noise ratios using a Fourier transform spectrometer. Many bands of the A 2Pi-->X 2Sigma+ and B' 2Sigma+-->X 2Sigma+ electronic transitions of 24MgH were analyzed; the new data span the v' = 0-3 levels of the A 2Pi and B'2Sigma+ excited states and the v''=0-11 levels of the X 2Sigma+ ground electronic state. The vibration-rotation energy levels of the perturbed A 2Pi and B' 2Sigma+ states were fitted as individual term values, while those of the X 2Sigma+ ground state were fitted using the direct-potential-fit approach.

The ACE-MAESTRO instrument on SCISAT: description, performance, and preliminary results.

The Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (MAESTRO) instrument on the SCISAT satellite is a simple, compact spectrophotometer for the measurement of atmospheric extinction, ozone, nitrogen dioxide, and other trace gases in the stratosphere and upper troposphere as part of the Atmospheric Chemistry Experiment (ACE) mission. We provide an overview of the instrument from requirements to realization, including optical design, prelaunch and on-orbit performance, and a preliminary examination of retrievals of ozone and NO(2).

Simultaneous measurements of visible (400-700 nm) and infrared (3.4 microm) NO(2) absorption.

Laboratory measurements of NO(2) absorption were obtained in the visible (400-700 nm) and mid-infrared (3.4 mum) regions simultaneously using SCISAT-1's ACE-FTS (atmospheric chemistry experiment-Fourier transform spectrometer) and MAESTRO (measurement of aerosol extinction in the stratosphere and troposphere retrieved by occultation) spectrometers. An intercomparison of these measurements was used to verify the consistency between the HITRAN 2004 3.