New analysis of the C2 Ballik-Ramsay system from flame emission spectra

The C₂b³Σ_g^? → a³Π_u Ballik-Ramsay system has been studied through emission flame spectra recorded with a Fourier transform interferometer. The 14 bands 0-0, 1-0, 1-1, 2-0, 2-1, 3-0, 3-1, 3-2, 4-1, 4-2, 5-2, 5-3, 6-3, and 7-4 were identified in the 4850- 9900-cm^?1 spectral range. They have been reduced to molecular constants using an iterative, nonlinear, least-squares method. Rotational perturbations, observed in the b³Σ_g^?v = 0, 1, 2, 5, and 6 levels, have been reduced. Dunham coefficients are obtained for both the b³Σ_g^? and a³Π_u states.     

Infrared emission of 12C16O, 13C16O,and 12C18O

The combination of a new high-resolution grating spectrometer and a spontaneous emission source has made it possible to measure precisely the 1 → 0, 2 → 1, and 2 → 0 transitions of ¹²C¹⁶O relative to the accurately known ¹²C¹⁶O laser lines which have been referred to pure frequency standards by Eng et al. The 1 → 0 and 2 → 0 band centers agree to within 0.0002 cm^?1 with those measured relative to wavelength standards by Fourier transform spectroscopy (FTS). From a weighted simultaneous fit to the FTS-absorption, FTS-flame, our grating-emission, and microwave results, a set of calculated line positions was obtained for the 1 → 0, 2 → 1, and 2 → 0 transitions of ¹²C¹⁶O. The absolute accuracy of these line positions is believed to be ±0.0005 cm^?1 and we propose that the lines can be used as secondary wavenumber standards in the infrared.The spontaneous emission sequences v′ → (v′ ? 1) were measured for ¹²C¹⁶O up to v′ = 20, for ¹³C¹⁶O up to v′ = 11 (using a ¹³C-enriched sample), and for ¹²C¹⁸O up to v′ = 4 (in natural abundance). Internally consistent sets of Dunham coefficients were calculated from the best available data for the molecules of ¹²C¹⁶O, ¹³C¹⁶O, and ¹²C¹⁸O.     

Fourier spectroscopy of the Asundi system (a′3Σ+-a3Π) of 13C16O

The Asundi system (a′³Σ⁺-a³Π) of ¹³C¹⁶O has been studied between 3500 and 12 000 cm⁻¹ by high-resolution Fourier transform spectroscopy. The 10 bands, 0-0, 0−1, 1−0, 1−1, 1−2, 2−0, 2−1, 3−0, 4−0, and 4−2, were analyzed taking into account the strong perturbations appearing in the a′³Σ⁺ (v = 0,…,4) levels. Accurate perturbation parameters were obtained for all interacting states.     

Fourier transform spectroscopy of CO2 and OCO in the 3800-8500 cm region and the global modeling of the absorption spectrum of CO2

The absorption spectrum of the ¹⁸O enriched carbon dioxide has been recorded at Doppler limited resolution with a Fourier transform spectrometer in the spectral range 3800-8500 cm⁻¹. Seventeen cold bands (14Σ-Σ and 3Σ-Π) and nine hot bands (9Π-Π) of ¹²C¹⁸O₂, nineteen cold bands (18Σ-Σ and 1Σ-Π) and eighteen hot bands (6Σ-Σ, 9Π-Π and 3Δ-Δ) of ¹⁶O¹²C¹⁸O have been observed. Among them, 14 ¹²C¹⁸O₂ bands and 12 ¹⁶O¹²C¹⁸O bands are observed for the first time. The spectroscopic parameters G_v, B_v, and centrifugal distortion constants, have been determined for all observed bands. Effective Hamiltonian parameters for the ¹²C¹⁸O₂ isotopic species are retrieved from the global fitting of the observed line positions presented in this paper and collected from the literature. As the result, 65 obtained effective Hamiltonian parameters reproduce 5443 observed line positions of 73 ¹²C¹⁸O₂ bands with RMS = 0.00145 cm⁻¹.     

Rotational and vibrational temperatures of electronically excited BiN radicals in a chemiluminescent flame

Rotational and vibrational temperatures of electronically excited BiN radicals in a low-pressure Bi_x+N/N₂*/N₂+Ar chemiluminescent flame have been deduced from high-resolution Fourier-transform emission spectra. Bands of three electronic transitions, a³Σ⁺(a₁1)→X¹Σ⁺(X0⁺), b⁵Σ⁺(b₁0⁺)→X¹Σ⁺(X0⁺), and b⁵Σ⁺(b₁0⁺)→a ³Σ⁺(a₁1), were analysed to determine the optical temperatures in the a³Σ⁺(a₁1) and b⁵Σ⁺(b₁0⁺) states. The rotational temperatures characterising the rotational populations in the a₁1, v=0 and 1 states were determined from the a₁→X, 0-2, 0-3, 0-4, 1-1, and 1-2 bands. The b₁→X, 0-8 and 0-11 bands, and the b₁→a₁, 0-0 bands served to determine the rotational temperature of the radicals in the b₁0⁺, v=0 state. The temperatures derived from the various bands and transitions were well consistent and the mean rotational temperature was determined to be 353±18 K, which is close to the translational temperature of the gas.Vibrational temperatures of the radicals in the a₁1 and b₁0⁺ states were derived from band intensities of the a₁→X and from the b₁→X as well as b₁→a₁ systems, respectively. The Franck-Condon factors needed were calculated with RKR potentials deduced from literature values of the rotational and vibrational constants in the three states involved. The a₁1 vibrational temperature (336±21 K) was close to the rotational temperature, while the b₁0⁺ vibrational temperature (438±36 K) differed, likely due to the previously observed perturbation of the b₁0⁺ state.     

The C1 IIg-A1 IIu Emission Spectrum of 12C13C

A few bands of the C¹II_g -A¹II_u system of ¹²C¹³C molecule have been photographed and five of them have been rotationally analyzed. Molecular constants for v = 0, 1 and 2 in the C¹ II_g and in A¹II_u states have been obtained using a nonlinear least-squares procedure in which all analyzed bands were fitted simultaneosly.     

The emission spectrum of 13C16O2 near 4.5 μm

The emission spectrum of ¹³C¹⁶O₂ near 4.5 μm, the ν₃ transition region, was measured in high resolution. The sequence 00v₃ → 00(v₃ ? 1) was measured to v₃ = 9, 01¹v₃ → 01¹(v₃ ? 1) to v₃ = 6, and 02²v₃ → 00²(v₃ ? 1) to v₃ = 3. Several bands involving Fermi resonant Σ state were also observed. The data were analyzed and spectroscopic constants were determined for all bands identified.     

Diagnosis of OH radical by optical emission spectroscopy in a wire-plate bi-directional pulsed corona discharge

The emission spectrum of the molecule OH (A²Σ→X²Π, 0–0) during a high-voltage, bi-directional pulsed corona discharge consisting of a gas mixture of N₂ and H₂O in a wire-plate reactor has been successfully recorded under severe electromagnetic interference at atmospheric pressure. The relative vibrational populations and the vibrational temperature of N₂ (C, v′) have also been determined. Due to the difficulty of determining the exact overlapping spectral line shape function of the OH (A²Σ→X²Π, 0–0) and the Δv=+1 vibrational transition band of N₂ (C³Π_u→B³Π_g), a practicable Gaussian form is used for calculating the emission intensity of OH (A²Σ→X²Π, 0-0) and the Δv=+1 vibrational transition band of N₂ (C³Π_u→B³Π_g). The emission intensity of OH (A²Σ→X²Π, 0–0) has been evaluated with a satisfactory accuracy by subtracting the emission intensity of the Δv=+1 vibrational transition band of N₂ (C³Π_u→B³Π_g) from the overlapping spectra. The relative population of OH (A²Σ) has been obtained by the emission intensity of OH (A²Σ→X²Π, 0–0) and Einstein's transition probability. The influences of peak voltage, pulse repetition rate and O₂ flow rate on the relative population of OH (A²Σ) radicals have also been investigated. We found that the relative population of OH (A²Σ) rises with an increase in both the peak applied voltage and the pulse repetition rate. When oxygen is added to an N₂ and H₂O gas mixture, the relative population of OH (A²Σ) radicals decreases exponentially with an increase in added oxygen. The main physicochemical processes involved are also discussed in this paper.     

Absolute Line Intensities in Acetylene: The 1.5-μm Region

We measured 305 absolute line intensities in the ν₁+ν₃(Σ⁺_u)-0(Σ⁺_g) band of ¹²C₂H₂ and ¹³C¹²CH₂ and the ν₁+ν₂+(ν¹₄+ν⁻¹₅)⁰(Σ⁺_u)-0(Σ⁺_g), ν₁+ν₃+ν¹₄(Π_g)-ν¹₄(Π_g), and ν₁+ν₃+ν₅¹(Π_u)-ν₅¹(Π_u) bands of the main isotopomer, all observed near 1.5 μm. The absolute intensity of these bands are respectively 6.4882 (34), 0.12337 (10), 0.083746 (71), 0.58771 (28), and 0.32126 (11) cm⁻² atm⁻¹ at 296 K. In addition, we also determined Herman-Wallis factors for the first time in this spectral region.     

Visible and near infrared emission spectra of PCl excited in the reaction of Ar(3P2, 0) with PCl3: Vibrational analysis of PCl A3Π → X3Σ− and b1Σ+ → X3Σ−

Two band systems of PCl, A³Π_r → X³Σ^? and b¹Σ⁺ → X³Σ^?, have been observed from the reaction of $\text{Ar}\text{(}{}^3\text{P}{}_{\mathrm{2,\; 0}}\text{)}$ with PCl₃ at pressures of 1–2 Torr. Seventy-eight bands of P³⁵Cl and 31 bands of P³⁷Cl in the region 4000–6000 Å have been assigned to the A³Π_r → X³Σ^? system and include levels with v′ = 0, 1, 2 and v″ = 3–18. The ground state numbering was obtained from a study of the vibrational isotope effect. The (0,0) sequence of the b¹Σ⁺ → X³Σ^? system occurs near 8200 Å and has been observed up to v′ = 10. Vibrational constants for all three states are derived from least-squares fits of the measured bandhead wavenumbers. The A ← X absorption system of PCl reported by Basco and Yee in flash photolysis of PCl₃ was not observed, and is probably due to absorption to a Rydberg state of PCl.     

Band analysis of the Swan system (d3Πg-a3Πu) of 13C2 and 12C13C molecules

The emission spectrum of the d³Π_g-a³Π_u system (Swan bands) due to ¹³C₂ and ¹²C¹³C molecules has been obtained in a low pressure hollow cathode discharge through a mixture of argon and benzene containing enriched ¹³C (90%). The spectrum was photographed on a 3.4-m Ebert spectrograph (reciprocal dispersion 0.54 Å mm^?1 in the first order). Isotope effect measurements have been carried out to determine the shift between isotopic bands and those emitted by ordinary molecules. The rotational analysis of six ¹³C₂ bands and three bands of ¹²C¹³C has been performed and molecular constants were derived.     

Magnetic rotation observation of the C2b3Σg− ← a3Πu transition using a color center laser

The magnetic rotation observation of the C₂b³Σ_g^? ← a³Π_u Ballik-Ramsay system using a color center laser is reported. This is the first detection of this system in absorption. Three bands, 0 ← 1, 1 ← 2, and 2 ← 3, were identified in the spectral range 3650–4030 cm^?1. The last two bands were observed for the first time. In magnetic rotation many satellite lines (ΔN ≠ ΔJ) which would be very weak in normal absorption have been observed with intensity comparable to the main branch lines. This permits a slight improvement in the accuracy of some of the fine structure constants. A variety of lineshapes are observed for the various branches by magnetic rotation. Because the b³Σ_g^? fine structure is small, giving a partial overlap, the peak frequency of a magnetic rotation signal usually does not correspond to the center frequency of the normal absorption signal of that transition. A computer program has been written to predict magnetic rotation lineshapes and obtain the peak frequency displacements. Various observed and calculated lineshapes are displayed and compared.     

High-resolution Fourier transform infrared spectra of 12C32S, 12C33S, 12C34S,and 13C32S

The v = 1-0 infrared absorption bands of the ¹²C³²S, ¹²C³³S, ¹²C³⁴S, and ¹³C³²S isotopes and the v = 2-1 “hot” band of ¹²C³²S all in the ground electronic state were measured using a high-resolution Fourier transform spectrometer coupled to a long-path absorption cell. P- and R-branch transitions, up to J = 41 for ¹²C³²S, have been measured at 0.004 cm⁻¹ unapodized resolution. Rotational and centrifugal distortion parameters which are improved over those obtained in previous diode laser measurements for the less abundant ¹²C³³S and ¹³C³²S isotopes are reported. Improved v = 1-0 band origins of the various isotopes are also reported. Analysis included published microwave data along with the present IR measurements. The present results are compared with previous infrared diode laser, Fourier transform spectrometer, and microwave measurements.     

Relative partial photoionization cross-sections and photoelectron branching ratios of ethylene

Relative partial photoionization cross-sections and photoelectron branching ratios of the valence bands (~10–25 eV binding energy) of ethylene are reported over the photon energy ranges 18–100 eV and 21–100 eV, respectively. The four lowest ionization energy bands (1b⁻¹_1u, 1b⁻¹_1g, 3a⁻¹_g, and 1b⁻¹_2u) show monotonic cross-section decreases with photon energy from 33 eV, the 1b⁻¹_1u CC π band showing the least rapid decline. In contrast, the 2b⁻¹_3u and 2a⁻¹_g bands show almost constant cross-sections up to ~50 eV photon energy, followed by similar, although slower, monotonic decreases. This is attributed to the substantial carbon 2s character of the 2b_3u and 2a_g orbitais. The cross-section behaviour of all bands is interpreted with the aid of SCF-LCAO-MO calculations on the neutral molecule using the Gaussian-80 series of programs.     

The infrared spectra of 12C32S, 12C34S, 13C32S,and 12C33S

Using a tunable diode laser spectrometer, the infrared absorption spectra of four isotopic species of carbon monosulfide have been observed in the positive column of a dc discharge of CS₂ and Ar. The wavenumbers of 115 vibration-rotation transitions between 1180.5 and 1266.1 cm^?1 have been measured. These lines were assigned to the 1-0, 2-1, 3-2, and 4-3 bands of ¹²C³²S, the 1-0 and 2-1 bands of ¹²C³⁴S and ¹³C³²S, and the 1-0 band of ¹²C³³S. These new data have been combined with the previous infrared and microwave results to determine Dunham coefficients (Y_ij), the Dunham potential expansion constants (a₀,a₁,a₂,a₃, and a₄), and the classical turning points by the RKR method.     

Investigation of N 2 + (C 2Σ u + → X 2Σ g + fluorescence excited through auger decay of the 1s −1π* resonance

A theoretical investigation of N ₂ ⁺ (C ²Σ _u ⁺ → X ²Σ _g ⁺ molecular fluorescence excited through the Auger decay of the 1s ^?1π* resonance is carried out. The fluorescence cross sections are calculated with due regard for the dependence of the matrix element of the C → X dipole transition on the internuclear distance, the interference between channels of excitation via different vibrational levels v _r of the 1s ^?1π* resonance, the rotational structure of the fluorescence band, and the predissociation of the N ₂ ⁺ C ²Σ _u ⁺ v′ ≥3) states. The calculated cross sections are in good agreement with the experimental results of recent measurements. The results of the calculations have demonstrated that the observed dependence of the cross section of the (C ²Σ _u ⁺ (v′) → X ²Σ _g ⁺ (v″) fluorescence on the excitation energy and the fluorescence wavelength for a group of bands with equal values of the difference Δv = v′ ? v″ is associated with transitions between the vibrational levels of the electronic states involved in the excitation and subsequent cascade decay of the 1s ^?1π* resonance: N₂ (v ₀ = 0) → N*₂(1s ^?1π*(v _r)) ? N ₂ ⁺ : (C ²Σ _u ⁺ (v′) → X ²Σ _g ⁺ (v″).     

Study of isotopic 13C2 bands of the Deslandres-D'Azambuja system

The emission bands of the Deslandres-D'Azambuja system of ¹³C₂ have been obtained in the region 320–450 nm using a source containing enriched ¹³C. Measured line positions of the 2-0, 2-1, 1-0, 0-0, 1-1, 1-0, 2-1, and 3-2 bands were fitted by a least-squares procedure to determine the rotational constants and the origin for each band. The fitted origins were used as input in calculation of the vibrational constants for both C¹Π_u electronic states involved in the transition.