The ion-molecule reaction O+ (4S) + N2(X1Σ+) → NO+ (X1Σ +, v′) + N(4S) and the predissociation of the A2Σ+ and B2Π states of N2O+

The potential energy surfaces (PESs) for several electronic states involved in the reaction O⁺ (⁴S) + N₂(X¹Σ⁺) → NO⁺ (X¹Σ ⁺, v′) + N(⁴S) and the role of the ionic N₂O⁺ intermediate have been investigated by ab initio calculations. The ⁴A″ PES, which correlates with the ground state educts, has a barrier of about 1 eV, and therefore at low collision energies the reaction cannot take place adiabatically on this surface. However, the spin-orbit coupling in the entrance channel allows the system to pass into the Renner-Teller system of the X² Π electronic ground state of the N₂O⁺ intermediate. The reaction then proceeds on these surfaces up to the region in the exit channel where a similar coupling allows it to reach the product quartet asymptote. At collision energies higher than about 1 eV, the reaction proceeds mainly on the adiabatic PES of the ⁴A″ state. The A²Σ⁺ state of N₂O⁺ predissociates via a vibronic coupling with the B²Π state, and in bent structures via a spin-orbit coupling with the ⁴A″ component of the ⁴II state. The electronic structure of the B²Π state is found to be of crucial importance for the understanding of the reactive processes in low lying electronic states of N₂O⁺.     

Rovibrational transition properties of the X1Σ+ and A1Π states of carbon monosulfide

Carbon monosulfide was detected in outer space by rovibrational spectroscopy of the X ¹Σ⁺ state and A ¹Π – X ¹Σ⁺ system. This work calculated the potential energy curves and dipole moment functions of the X ¹Σ⁺ ₀₊ and A ¹Π₁ states, and computed the transition dipole moments between the two states employing the CASSCF method, followed by the valence icMRCI approach. Core-valence correlation and scalar relativistic corrections were included. The extrapolation of potential energies to the complete basis set limit was performed. The spin-orbit coupling effect was included. The Einstein A coefficients, band origins, and oscillator strengths were calculated for the rovibrational transitions when J?≤?150. The rovibrational transitions of the X ¹Σ⁺ ₀₊ and A ¹Π₁ states became very weak when Δυ?≥?6. The Einstein A coefficients of vibronic emissions of the A ¹Π₁ – X ¹Σ⁺ ₀₊ system were large, indicating that the emissions were able to be measured easily through spectroscopy. Several rovibrational transitions of the A ¹Π₁ – X ¹Σ⁺ ₀₊ system were analysed in detail. The distribution of radiative lifetime varying as rotational quantum number was calculated. The results obtained in this work agree well with the available experimental values.     

Revised molecular constants and term values for the XΣ and AΠ states of NH

The vibration–rotation spectra of NH have been reinvestigated using laboratory spectra and infrared solar spectra recorded from orbit by the ACE and ATMOS instruments. In addition to identifying the previously unobserved 6–5 vibration–rotation band in the laboratory spectra, many additional high N rotational lines have been observed. By combining the new observations with the previously published data and recent far infrared data, an improved set of molecular constants and term values have been derived for the X³Σ⁻ and A³Π states.     

The X2Π and A2Σ+ states of FH+, ClH+ and BrH+: theoretical study of their g -factors and fine/hyperfine structures

Theoretical calculations on the fine, hyperfine and Zeeman (g-factor) parameters are reported for the X²Π and A²Σ⁺ states of FH⁺, ClH⁺ and BrH⁺. The fine-structure constants [spin–orbit (A), Λ-doubling (p, q) and spin–rotation constants (γ _Π, γ _Σ)] are evaluated up to second order (via SO/L couplings with several excited states) using a multireference configuration interaction (MRCI) method, a Breit–Pauli Hamiltonian and 6-311++(2d,2pd) basis sets. Hyperfine constants of magnetic and electric type [Frosch–Foley (a, b, c, d) and nuclear quadrupole (eQq ₀, eQq ₂)] are studied with density functional methods and various basis sets. Magnetic dipole moments (parameterized via g-factors) are calculated in second order like the fine structure constants. The situation is somewhat complex for X²Π since no less than five different g’s have to be evaluated in second order. In general, our results are in good agreement with those reported in the literature, mostly limited to the ground state. Our calculations confirm that, at equilibrium, all second-order properties are dominated by the couplings between the electronic states X and A.     

Spin-orbit splitting in the X2Π, a4Π, B2Π and H2Π electronic states of the NS radical

A model calculating the laser fields at a flat structureless surface taking into account the surface photoelectric effect is presented. The photon is p or transverse magnetic linearly polarized, continuous and its wave length is long, i.e. λ _vac  ≥ 12.4 nm. The sharp rise of the electron density at the interface generates an atomic scale spatial dependence of the laser field. In real space and in the temporal gauge, the vector potential A of the laser is obtained as a solution of the classical Ampère-Maxwell and the material equations. The susceptibility is a product of the electron density of the material system with the surface and of the bulk tensor and non-local isotropic (TNLI) polarizability. The electron density is obtained quantum mechanically by solving the Schrödinger equation. The bulk TNLI polarizability including dispersion is calculated from a Drude-Lindhard-Kliewer model. In one dimension perpendicular to the surface the components \hbox{$\mathcal{A}_x(z,\omega)$} ?? _x (z,ω) and \hbox{$\mathcal{A}_z(z,\omega)$}?? _z (z,ω) of the vector potential are solutions of the Ampère-Maxwell system of two coupled integro-differential equations. The model, called vector potential from the electron density-coupled integro-differential equations (VPED-CIDE), is used here to obtain the electron escape probability from the power density absorption, the reflectance, the electron density induced by the laser and Feibelman’s parameters d _∥ and d _⊥. Some preliminary results on aluminium surfaces are given here and in a companion paper the photoelectron spectra are calculated with results in agreement with the experiment.     

The S21 lines of the A2Σ+ (v′ = 1)←X2Π (v″ = 0) transitions of OH and OD

The S₂₁ lines of the OH radical for the A²Σ⁺ (v′ = 1)←X²Π (v″ = 0) transition have been observed in the 278–280 nm region from the laser-excitation spectrum. The OH radical was generated from either the H + NO₂ or the H + O₃ reaction in a flow system and the fluorescence passing through a 309.6 nm interference filter was detected with a photomultiplier-boxcar integrator arrangement. The weak S₂₁ lines were observed at laser energies above 0.2 mJ. The observed peak wavenumbers are in excellent agreement with those predicted for the S₂₁ bands of the A (v>′ = 1)←X (v″ = 0) transition from the known spectroscopic parameters. Observation of the corresponding S₂₁ system for OD in the 286.0–286.9 nm region further confirms this assignment. The relative absorption cross-sections of about one-tenth those of the P₁ lines are in good agreement with theoretical considerations.     

Radiative lifetime measurements of vibrational levels of Cl2 + A 2Π u

The radiative lifetimes of several vibrational levels of Cl₂ ⁺ A ²Π _u are measured by a novel technique. A uniform electric field extracts the ions from the observation region of a spectrometer, and the decrease of fluorescence signal as a function of the electric field strength is measured to obtain the radiative lifetime. Measurements are made on 20 different vibronic bands of the Cl₂ ⁺ A ²Π _u -X ²Π _g system, and the results are compared with other methods. An attempt is made to correlate the results with the highly perturbed spectroscopic nature of the A ²Π _u electronic state.     

Characterization of the [Xtilde] 1Σ+ à 3Π and à 1Π electronic states of BBO

The three lowest-lying electronic states, [Xtilde] ¹Σ⁺, à ³II and à ¹II, of the linear BBO molecule have been systematically investigated using ab initio electronic structure theory. The equilibrium structures and physical properties including dipole moments, vibrational frequencies and associated infrared intensities, Renner parameters and energetics for the three states of BBO have been determined employing SCF, CISD, CCSD and CCSD(T) levels of theory and a wide range of basis sets. The ground state of BBO presents a degenerate real bending frequency, while the à ³II and à ¹II states show two distinct real bending frequencies due to the Renner-Teller interaction. The bending motion of the à ¹II state was analysed using the equation-of-motion (EOM)-CCSD and EOM-CC3 techniques in order to avoid possible variational collapse to a lower-lying state. The [Xtilde] ¹Σ⁺-à ³II separation was predicted to be T ₀ = 16.6 kcal mol^?1 (5800 cm^?1, 0.719 eV) at the cc-pVQZ CCSD(T) level of theory. With the cc-pVQZ EOM-CC3 method the [Xtilde] ¹Σ⁺-à ¹II splitting was predicted to be T ₀ = 48.0 kcal mol^?1 (16 800 cm^?1, 2.08 eV), which is in good agreement with the experimental value of T ⁰ = 46.6 kcal mol^?1 (16 300 cm^?1, 2.02 eV). The Renner parameters and averaged harmonic frequencies of the bending mode were determined to be ? = 0.184 and ω₂ = 363 cm^?1 for the à ³II state, and ? = 0.246 and ω₂ = 383cm^?1 for the à ¹II state. The theoretical [Xtilde] ¹Σ⁺ state harmonic B-B stretching frequency ω₃ = 636 cm^?1 is somewhat higher than the experimental estimate of 582 cm^?1 and the predicted à ¹II state harmonic B-B stretching frequency ω₃ = 861 cm^?1 is significantly higher than the experimental estimate of 440 cm^?1     

Analysis of the bands of the B2Σ+-X2Σ+ transition in 12C16O+ and 13C16O+

The First Negative bands of ¹²C¹⁶O⁺ and ¹³C¹⁶O⁺, in the spectral region 40 000–46 000 cm⁻¹, have been photographed at a resolution sufficient to resolve the spin-doubled components. These data for ¹²C¹⁶O⁺, along with previously reported data of the same transitions, as well as microwave transitions of ¹²C¹⁶O⁺ in the ground state, have been explicitly included in a least-squares fit to determine the most precise set of molecular constants to date for the B²Σ⁺ and X²Σ⁺ states of ¹²C¹⁶O⁺. Furthermore, we report a rotational analysis of the First Negative bands of ¹³C¹⁶O⁺ for the first time. Several molecular constants characterizing ¹³C¹⁶O⁺ in the B²Σ⁺ and the X²Σ⁺ states, including spin-doubling parameters, have been determined.     

Spin-orbit effects in the ground X2Π state and two low-lying excited valence states B2Π and L′2Φ for NO

The potential energy curves and spectroscopic constants B _e , ω _e , ω _e χ _e , α _e , D _e of the six Ω states (X ²Π_1/2, ? 3/2, B ²Π_1/2, ? 3/2 and L ^′2Φ_{5/2,   7/2}) of the NO radical molecule were calculated using spin-orbit multi-configuration quasi-degenerate perturbation theory (SO-MCQDPT). The spin-orbit coupling effect was considered via the state interaction approach with the full Breit-Pauli Hamiltonian. The spin-orbit splitting energy between the X ²Π_1/2 and X ²Π_3/2 states of the NO radical is 129.61 cm^-1, which agrees reasonably well with the experimental value of 123.13 cm^-1. For the B ²Π_{1/2,   3/2} states, the spin-orbit coupling (SOC) splitting energy is 35.99 cm^-1, the corresponding experimental value is 31.7 cm^-1. The SOC splitting value of the L ^′2Φ_{5/2,   7/2} states was calculated to be 103.2 cm^-1. The spectroscopic constants R _e , ω _e , ω _e χ _e , B _e , α _e , D _e are in reasonable agreement with available experimental and theoretical data for the six Ω states.     

Measurements of the line strengths,N2− and O2-broadened half-widths in the ν3, ν1+2ν2 and 2ν1 bands of 14N2 16O at room temperature

The line strengths, N₂? and O₂-broadened half-widths in the ν₃, ν₁+2ν₂ and 2ν₁ bands of ¹⁴N₂ ¹⁶O were determined from spectra obtained by a high-resolution Fourier transform spectrometer at room temperature. The squared vibrational transition dipole moments and the coefficients of the Herman–Wallis factor were also determined for these bands. The squared vibrational transition dipole moments for these bands agreed with the values of HITRAN and high-resolution experiments within 6%. The N₂? and O₂-broadened half-widths were in agreement with the results of recent high-resolution experiments. The air-broadened half-widths were calculated using the smoothed N₂? and O₂-broadened half-widths and compared with the compiled values in the HITRAN database.     

High-precision laser and RF spectroscopy of the spin-rotation and HFS interactions in the X2Σ+ and B2Σ+ states of LaO

The spin-rotation and hyperfine interactions in the X²Σ⁺ and B²Σ⁺ electronic states of ¹³⁹La¹⁶O have been studied using Doppler-free laser-induced fluorescence and molecular-beam laser-rf double resonance. Observations were made for several values of v and many values of N, allowing evaluation of the principal interaction strengths and their N and v dependences for both the X and B states. The results are compared with earlier results for the isoelectronic system ¹³⁷Ba¹⁹F.     

Rotational Analysis of the 1–4 Band of the B 2Σ+–X 2Σ+ System of 14C16O+

ABSTRACT

High-resolution emission spectrum of the 1–4 band of the B ²Σ⁺–X ²Σ⁺ transition of ¹⁴C¹⁶O⁺ was observed for the first time by conventional emission spectroscopy. The band spectrum was excited in a water-cooled Geissler lamp filled with commercial gaseous carbon monoxide enriched in about 80% of the radiocarbon ¹⁴C. A rotational analysis has been carried out and obtained molecular constants have been merged with previously published data for the B ²Σ⁺–A ²Π_i and A ²Π_i–X ²Σ⁺ transitions. The principal equilibrium constants for the ground X ²Σ⁺ state obtained from this work are ω_e = 2121.7726(98), ω_e x _e = 13.9055(27), B _e = 1.815290(30), α_e = 1.6594(33) × 10^?2, and γ_e = ? 0.377(73) × 10^?4 cm^?1. Also, presently known experimental equilibrium molecular constants of the X ²Σ⁺ states of the CO⁺ isotopic molecules are summarized and isotopic dependence of the B _e and ω _e constants is discussed.