Time-resolved Fourier transform emission spectroscopy of AΠ-XΣ infrared transition of the CN radical

The A²Π-X²Σ⁺Δv = −3 bands of the ¹²C¹⁴N radical have been observed by time-resolved Fourier transform spectroscopy in the 1850-3100 cm⁻¹ region with a wavenumber resolution of 0.025 cm⁻¹. The radical was produced in a pulsed positive column discharge in a cyanogene and helium mixture. Seven bands of v = 0-3, 1-4, 2-5, 3-6, 4-7, 5-8, and 6-9 were analyzed to give the molecular constants of each state by least-squares fitting of 801 lines. The pulsed discharge was found to be efficient for production of CN in the excited A²Π state. The vibrational excitation temperature was determined to be 6680 ± 835 K and 6757 ± 534 K for the A²Π and X²Σ⁺ states, respectively. The population of the A²Π was found to be 4% of that of the X²Σ⁺ state in the time after turning off the discharge.     

Deperturbation of DΠ v = 4 level of ScF molecule: Characterization of the Π perturber from analyses of DΠ-XΣ 4-2 and DΠ-AΔ 4-4 LIF transitions

High resolution emission spectra of ScF molecule have been observed in the region of 21 120-21 300 cm⁻¹ and of 15 640-15 710 cm⁻¹. The rotational structures in 4-2 band of D¹Π-X¹Σ⁺ and in 4-4 band of D¹Π-A¹Δ were assigned. Rotational analysis reveals the presence of localized perturbations in the upper state D¹Π v = 4 level at different values of J for the two parity sublevels, e and f. These perturbations are interpreted as the consequence of a spin-orbit interaction between D¹Π state and a triplet state of ³Π symmetry. A matrix model describing the energies within the two interacting levels, has been used to fit term-values. Spectroscopic constants are obtained for A¹Δ v = 4, D¹Π v = 4 and for the ³Π perturbing level. The magnitude of the spin-orbit interaction is estimated.     

A Reanalysis of theA1Π–X1Σ+Transition of AlBr

TheA¹Π–X¹Σ⁺transition of aluminum monobromide (AlBr) near 2800 Å was recorded using a Bruker IFS 120 HR Fourier transform spectrometer at nominal resolutions of 4 and 0.03 cm⁻¹. All bands showP,Q, andRbranches and all are degraded to longer wavelengths. The 0–0 band is the most intense and the Δv= 0 sequence dominates the observed spectrum. Each band appears doubled due to the natural isotopic abundances of⁷⁹Br (50.69%) and⁸¹Br (49.31%). Band origin shifts due to isotopic substitution of bromine were examined to confirm the assignments of isotopic species. The rotational structure of the 0–1, 1–2, 0–0, 1–1, and 2–2 bands was assigned and fitted. These data were merged with previously reported photographic data for the 1–0, 2–1, 3–2, 2–0, and 3–1 bands and also infrared and microwave measurements to provide an improved set of constants for both electronic states. The rotational constants for each vibrational level in theX¹Σ⁺state vary smoothly with increasing vibrational quantum number and thus an expansion of the constants in terms of equilibrium values is recommended. An expansion of theA¹Π rotational constants in terms of equilibrium values is not recommended as the distortion constants do not change smoothly with increasing vibrational quantum number. Therefore, the rotational constants for theA¹Π state were determined for each individual vibrational level. This approach leads to vastly improved vibrational constants for theA¹Π state by reducing correlations between rotational and vibrational constants. This problem is serious for theA¹Π state owing to severe departures from harmonic behavior in thev= 2 andv= 3 levels.     

Time-resolved Fourier transform infrared spectroscopy: Application to pulsed discharges

Time-resolved Fourier transform spectroscopy (TR-FTS) is reviewed, with emphasis on synchronous FTS using continuously scanning interferometers. By using a high-resolution Bruker IFS 120 HR, a TR-FTS method has been developed with the help of a microcontroller SX, where a maximum of 64 time-resolved data are recorded with a preset time interval in a single scan of the interferometer. The time resolution is 1 μs, limited by the response time of the detector system used. This method has been applied to a pulsed discharge in an Ar and H₂ mixture to observe time profiles of ArH⁺ and ArH emission spectra. Electronic transitions of He₂ have been observed in the infrared region with this method, and from the time profiles, He₂ in Rydberg states with higher energy than the b³Π state is found to be produced efficiently in afterglow plasma. Fifteen bands in the 2300-8000 cm⁻¹ region have been assigned by using previously reported data from the optical region. A new band from the 5f state has been assigned for the first time through the 5f-4d band in the 2600 cm⁻¹ region.     

Infrared emission studies of the AΣ-XΠ electronic transition of the SiC radical

The gas phase infrared emission spectrum of the A³Σ⁻-X³Π electronic transition of SiC has been observed using a high resolution Fourier transform spectrometer. Three bands ν′ − ν″ = 0-1, 0-0, and 1-0 have been observed in the 2770, 3723, and 4578 cm⁻¹ regions, where the 0-1 and 0-0 bands were observed for the first time. The SiC radical was generated by a dc discharge in a flowing mixture of hexamethyl disilane [(CH₃)₆Si₂] and He. A total of 1074 rotational transitions assigned to the 0-1, 0-0, and 1-0 bands have been combined in a simultaneous analysis with previously reported pure rotational data to determine the molecular constants for SiC in the two electronic states. The principal equilibrium molecular constants for the A³Σ⁻ state are: B_e = 0.6181195(18) cm⁻¹, α_e = 0.0051921(20) cm⁻¹, r_e = 1.8020884(26) Å, and T_e = 3773.31(17) cm⁻¹, with one standard deviation given in parentheses. The effect of a perturbation was recognized between the ν = 4 level of X³Π and the ν = 0 level of A³Σ, and the analysis was carried out to determine the interaction parameter between the two states.     

The 13C2 and 12C13C Ballik-Ramsay system

The infrared spectrum of the b³Σ⁻ → a³Π Ballik-Ramsay system has been observed for both ¹³C₂ and ¹²C¹³C isotopic species using high-resolution Fourier transform spectroscopy. Twelve bands: 0 → 0, 1 → 0, 1 → 1, 2 → 0, 2 → 1, 3 → 1, 3 → 2, 4 → 2, 4 → 3, 5 → 2, 5 → 3, 6 → 3 of ¹³C₂ and seven bands: 0 → 0, 1 → 0, 1 → 1, 2 → 0, 2 → 1, 3 → 1, 3 → 2 of ¹²C¹³C were identified in the spectral range 3500–12 000 cm⁻¹. Perturbations in the b³Σ⁻ (v = 0, 1, 2, 3) levels were reduced and accurate perturbation parameters derived from the analysis. A comparison with ab initio calculated spin-orbit coupling constants is presented.     

Diode laser spectrum of HCCl near 5 μm: The ν2 fundamental and accompanying hot bands

The CC stretching band ν₂ of iodoacetylene has been studied by tunable laser spectroscopy in the range of 2037–2071 cm^?1. The hot bands associated with the low-lying bending vibrations ν₄ and ν₅ were observed. For the Π-Π hot bands, the splitting caused l-type doubling was resolved for high J transitions. For the fundamental band the hyperfine splittings due to the ¹²⁷I nuclear quadrupole moment were clearly observed for R(0) and P(1) transitions. Combination of these diode laser spectra with the microwave data allows precise determination of the constants in the ground and excited vibrational states.     

Infrared and near infrared emission spectra of TeH and TeD

The vibration-rotation emission spectra for the X²Π ground state and the near infrared emission spectra of the X²Π_1/2-X²Π_3/2 system of the TeH and TeD free radicals have been measured at high resolution using a Fourier transform spectrometer. TeH and TeD were generated in a tube furnace with a DC discharge of a flowing mixture of argon, hydrogen (or deuterium), and tellurium vapor. In the infrared region, for the X²Π_3/2 spin component we observed the 1-0, 2-1, and 3-2 vibrational bands for most of the eight isotopologues of TeH and the 1-0 and 2-1 bands for three isotopologues of TeD. For the X²Π_1/2-X²Π_3/2 transition, we observed the 0-0 and 1-1 bands for TeH and the 0-0, 1-1, and 2-2 bands for TeD. Except for a few lines, the tellurium isotopic shift was not resolved for the X²Π_1/2-X²Π_3/2 transitions of TeH and TeD. Local perturbations with Δv = 2 between the two spin components of the X²Π state of TeH were found: X²Π_1/2, v = 0 with X²Π_3/2, v = 2; X²Π_1/2, v = 1 with X²Π_3/2, v = 3. The new data were combined with the previous data from the literature and two kinds of fits (Hund’s case (a) and Hund’s case (c)) were carried out for each of the 10 observed isotopologues: ¹³⁰TeD, ¹²⁸TeD, ¹²⁶TeD, ¹³⁰TeH, ¹²⁸TeH, ¹²⁶TeH, ¹²⁵TeH, ¹²⁴TeH, ¹²³TeH, and ¹²²TeH.     

Resonance-enhanced multiphoton ionization detection of a new 3Σ+-a3Π band system in CS

Resonance-enhanced multiphoton ionization has been used to detect absorption transitions from the nascent states of CS produced in the two-photon laser flash photolysis of CS₂. Transitions are seen from the a³Π state of CS to a previously unobserved ³Σ⁺ state. Rotational assignments of the (1, 0), (0, 0), (0, 1), and (0, 2) bands have been made; the derived constants for those bands are similar to those of the CS⁺ ion, in good agreement with the assumption that the upper electronic state is the 3sσ³Σ⁺ Rydberg state.     

The c.hfl-value of the NO δ(0, 0) band by the line absorption method

The resonance-line absorption method has been applied to the isolated but unresolved (0, 0) band of the NO δ system, C²Π - X²Π. The light source was the N + O radiative recombination afterglow in a discharge flow system. This is an optically-thin source of δ(0, 0) emission, with known rotational temperature and Doppler width, uncontaminated with overlapping ε bands. Corrections for effects of accidental line overlap within the band and perturbation between the C and B states have been applied in comparing observed and computed band fractional absorption curves. For the δ(0, 0) band, this comparison gives c.hfl = (2·2 ± 0·3) × 10^-3. Our result is compared with previous measurements obtained by four other independent methods.     

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.     

Fourier transform spectral study of BΣ-XΣ system of AlO

The spectrum of B²Σ⁺-X²Σ⁺ system of AlO has been recorded on BOMEM DA8 Fourier transform spectrometer at an apodized resolution of 0.05 cm⁻¹. Nineteen bands of the Δv = 1, 0, −1, and −2 sequences of this band system have been analyzed for the rotational structure. Out of which seven bands, viz. 3-2, 4-3, 2-3, 3-4, 4-5, 5-6 and 6-7 have been analyzed for the first time. The rotational lines of these 19 bands along with 20 earlier analyzed bands, a total of 7200 lines, have been fitted in a simultaneous least squares fit. The study has resulted in determining more precise vibrational and rotational constants of the two states. Because of the high resolution employed it became necessary to invoke H₀ and H₁ coefficients, and a fifth order term to explain the anomalous spin-doubling observed in the v″ = 5, 6 and 7 levels of the X²Σ⁺ state.     

The laser-induced fluorescence study of AΣ-XΠi band system of CuS

The laser-induced fluorescence excitation spectra of jet-cooled CuS molecules have been recorded in the energy range of 17 200-19 500 cm⁻¹. Fourteen observed vibronic bands have been assigned as three transition progressions: A²Σ⁻ (v′ = 0-4)-X²Π_3/2 (v″ = 0), A²Σ⁻ (v′ = 0-4)-X²Π_3/2 (v″ = 1), and A²Σ⁻ (v′ = 0-3)-X²Π_1/2 (v″ = 0). Spectroscopic constants of both the X²Π ground state and the A²Σ⁻ excited state of ⁶³CuS and ⁶⁵CuS were determined by analyzing their rotationally resolved spectra. Furthermore, the lifetimes of most observed bands were measured for the first time.     

Rotational analysis of the A2Σ+ → X2Π system of OT. Merged molecular constants for OT A2Σ+, v ≤ 4 and X2Π, v ≤ 3

The A²Σ⁺ → X²Π band system of OT was observed for the first time. Fourteen bands with 0 ≤ v′ ≤ 4 and 0 ≤ v″ ≤ 3 were photographed at high resolution and rotationally assigned. Fitted values of 18 effective parameters of the model Hamiltonians used to describe individual vibrational levels of the two states are determined by least-squares from the data of each band. Multiple determinations of the parameters are merged to obtain single-valued estimates of the same parameters, as well as Dunham coefficients describing their vibrational dependence.     

Franck-Condon factors and r-centroids of B-X, C-X and C-A band systems of AlO molecule

Using the high resolution Fourier transform spectrometer the B²Σ⁺-X²Σ⁺ band system of AlO molecule has been recorded. The rotational structure of eighteen bands belonging to B²Σ⁺-X²Σ⁺ transition of AlO have been analyzed which led to accurate rotational and vibrational constants of ground and excited states. A few bands, viz. (2, 1), (3, 2), (4, 3), (2, 3), (3, 4), (4, 5), and (5, 6) were analyzed for the first time. Using these constants, the Franck-Condon factors and r-centroids were computed for the bands of B-X, C-X and C-A band systems for the v′ = 0-8; v″ = 0-8 matrix using the method developed by Jarmain and Nicholls. The F-C factors and r-centroids obey the established relationships.     

Laser spectroscopy of the A-X transitions of CaOH and CaOD

The A-X transitions of gas phase CaOH and CaOD, produced in a low-pressure flow system, were studied by low- and high-resolution laser spectroscopy. The vibrational structure of the low-lying vibrational levels of both the A and X states were determined. A detailed rotational analysis of the (0, 0, 0)-(0, 0, 0) bands of the A-X system is presented. The spectra are well described by a²Π-²Σ model, where the molecule is linear in both states. A preliminary analysis of the (0, 1, 0)-(0, 1, 0) bands indicates that the Renner parameter ? of the A²Π electronic state is equal to 0.073(1).     

The B2Σ+ → A2Πi system of silicon nitride,SiN

The 440-nm violet-degraded ${}^2\text{Σ →}{}^2\text{Π}$ bands of SiN, which were previously assigned to a $\text{“K” → A}$ system, have been reanalyzed. These bands are shown to be Δv = 0, ±1 sequence bands of the B²Σ⁺ → A²Π system of SiN. The first reliable value of T_e(A²Π) = 994.4(1) cm^?1 has been obtained, and this determines the location of the D²Π and L²Π states with respect to the ground state. The B²Σ⁺, v = 7 and D²Π, v = 3 levels are shown to be mutually perturbing. A detailed study has been made of the perturbed X²Σ⁺, v = 8 level. The 6–8 band of the B → X system has been photographed at high resolution. A deperturbation of this band confirms T_e(A²Π), and provides the first experimental verification of the inverted nature of the A state.     

New spectroscopic studies of the Comet-Tail (AΠi-XΣ) system of the CO molecule

In the electronic emission spectrum of the ¹²C¹⁶O⁺ molecule, 11 bands of the Comet-Tail (A²Π_i-X²Σ⁺) system have been recorded and analyzed. Spin splitting in most of the observed lines of the 0-2, 1-0, 2-0, 2-1, 3-0, 4-0, 4-2, 6-0, 7-0, 7-1, and 8-1 bands, comprising nearly 3400 lines, has been recorded under high resolution by conventional spectroscopy. The rotational analysis of bands has been performed by nonlinear least-squares procedures and by means of effective Hamiltonians of Brown et al. and the rovibronic structure parameters have been obtained. The data of bands of the A-X system and earlier analyzed bands of the B-X and B-A systems have been merged together. As a result of this global fit, the state of information about the energy structure has been significantly enlarged for the A state and enlarged and improved for the X state. Also RKR potential curves for both states and Franck-Condon factors as well as r-centroids of the Comet-Tail system of CO⁺ have been calculated.     

On the cΠ (v = 0) state of carbon monoxide

A full analysis of the near infrared c³Π-b³Σ⁺ (0-0) band is given and term values for both states determined. The c³Π (v = 0) state was jointly analysed with the perturbing k³Π (v = 2) state and data from the c³Π-X¹Σ⁺ (0-0) transition and 3A band system were included. It is shown that the available data are consistent with the c³Π (v = 0) state having near Hund’s case b coupling with a spin-orbit constant of A = 0.45 ± 0.02 cm⁻¹, a homogeneous perturbation with the k³Π (v = 2) state, and Λ-type doubling arising predominantly from its interaction with the j³Σ⁺ state. A discrepancy with a more recent report of the 3A band system is identified and discussed. The perturbed b³Σ⁺ state term values are consistent with a previously reported five state interaction model.     

Rydberg series of NO converging to the ionic states b3Π, A1Π, and w3Δ

Rydberg series of NO in the 600–1000-Åregion were investigated by using a 6.65-m high-dispersion vacuum spectrograph. The previous β, γ (v = 0), and γ (v = 1) Rydberg series were extended up to n = 31, 31, and 28, respectively. From the analysis of these Rydberg series, accurate ionization energies were obtained: 133 565 ± 3 (16.5596 eV) for b³Π (v = 0); 147 811 ± 3 (18.3258 eV) for A¹Π (v = 0); 149 372 ± 3 cm^?1 (18.5193 eV) for A¹Π (v = 1) of NO⁺. A new Rydberg series converging to one of the triplet components in b³Π was identified, and the coupling constant of b³Π was estimated to be 35 ± 8 cm^?1. Higher members of two Rydberg series were newly observed in the 700–725-Åregion. From their series limits, 139 926 ± 3 and 141 160 ± 3 cm^?1, they were assigned to be the Rydberg series converging to the v = 3 and 4 levels of ω ³Δ in NO⁺.