Fourier transform high-resolution measurements on the 2 ← 0, 3 ← 0, 4 ← 0, 5 ← 0 infrared absorption bands of HI and DI

Fourier absorption spectra of HI and DI were recorded simultaneously in a very large spectral range and the results enabled the prediction of the 1 ← 0 band of TI. For the wavenumbers of most lines, the absolute accuracy was estimated to be better than 2 × 10^?7 × σ. The TI spectrum was calculated with an estimated precision of 20 × 10^?3 cm^?1 by extrapolation from the HI and DI spectra through a Dunham analysis corrected for the Born-Oppenheimer approximation. In the course of this experiment, Doppler-limited electricquadrupole hyperfine structures were detected for low J lines of the first overtone bands.     

Absolute wavenumber measurements of 1-0, 2-0, HF and 2-0, H35Cl,H37Cl absorption bands

Fourier absorption spectra of HCl and HF at room temperature permitted to measure 87 absolute wavenumbers. The absolute observed position of the P(6) line of the 1-0 band of HF is not in agreement with a recent heterodyne determination [3]. It is found equal to 110 725 739 ± 7.5 MHz.     

Infra-red absorption bands 1-0, 2-0, 3-0 and 4-0 of the two isotopic species D79Br and D81Br of deuterium bromide

High resolution spectra of the 1-0, 2-0, 3-0, and 4-0 infra-red absorption bands of the two isotopic species of deuterium bromide have been recorded up to very high J values. The equilibrium molecular parameters obtained in the analysis fit the 267 observed lines within their experimental uncertainties, and give precise calculated wavenumbers for some observed chemical laser lines of these molecules.     

Absorption intensities for the 4-0 through 7-0 overtone bands of HCl

We have measured the absorption intesities for a number of rotation-vibration lines in the 4-0 through 7-0 overtone bands of HCl utilizing a Fourier transform spectrometer and a 409.6 m path length White cell. Individual line strengths, band strengths, dipole matrix elements, and Herman-Wallis factors are presented.     

Self-broadening and shifting of HI lines in the 1-0 and 2-0 infrared bands

Pressure-broadening and -shifting coefficients of pure HI at room temperature have been determined from fits of high-resolution Fourier transform spectra in the fundamental and first overtone infrared bands. The results indicate that the measured widths are almost identical in both bands and decrease significantly with the rotational quantum number. On the contrary, the pressure-induced shifts show a strong dependence on both the rotational and vibrational states. These results are compared with predictions of a semi-classical model. The latter leads to calculated values in good agreement with measurements and shows that the broadening is dominated by electrostatic interactions due to the (permanent) electric dipole and quadrupole moments. On the contrary, the observed shifts cannot be explained without the introduction of a significant vibrationally dependent isotropic potential. The effects of line coupling between hyperfine components are also discussed although they are expected to be small and cannot be observed from the measured spectra. Finally, some tabulated values of calculated widths and shifts vs. quantum numbers and temperature are proposed. They should be useful for infrared sounding of HI amounts, particularly in the monitoring of the hydrogen production through the sulfur-iodine thermochemical cycle.     

Rotation-vibration analysis of the Coriolis-coupled ν5g, ν6g, ν8g and ν9 bands of H2CCO

Medium resolution infrared grating spectra of gaseous ketene, H₂CCO were recorded between 1000 and 400 cm^?1, both at instrument temperature (40°C) and with cooling (?40°C). Interferometric Fourier spectra were also measured at ?70°C with resolution 0.22 cm^?1 between 450 and 330 cm^?1. The K structure of the fundamentals ν₅, ν₆, ν₈, and ν₉ was assigned. These fundamentals are coupled by a-axis Coriolis interactions. These couplings were analysed on the symmetric top basis for setting up the perturbation matrix and by utilizing the K-dependent Coriolis shifts of levels. A preliminary analysis of the Coriolis intensity anomalies was also undertaken.Band center values from combination differences are $\text{ν}{}_5{}^0\text{= 587.30 (27)}$ and $\text{ν}{}_6{}^0\text{= 528.36 (39)}\text{cm}{}^{\mathrm{?1}}$. Synthetic spectra indicate the band origins of ν₈ and ν₉ to be close to 977.8 and 439.0 cm^?1, respectively. Estimates of Coriolis coupling constants obtained from synthetic spectra are $\text{ζ}{}_{58}{}^{\mathrm{a}}\text{= + 0.33 (5)}$, $\text{ζ}{}_{68}{}^{\mathrm{a}}\text{= + 0.714 (20)}$, $\text{ζ}{}_{59}{}^{\mathrm{a}}\text{= ? 0.774 (20)}$, and $\text{ζ}{}_{69}{}^{\mathrm{a}}\text{= ? 0.30 (2)}$. Approximate ratios of unperturbed vibrational transition moments obtained from spectral simulations are $\text{M}{}_8{}^0\text{:±iM}{}_5{}^0\text{:±iM}{}_6{}^0\text{:M}{}_9{}^0\text{≈ +2:?9:+10:+0.5}$.     

Measurements of pressure-induced shifts in the 1-0 and 2-0 bands of HF and in the 2-0 bands of H35Cl and H37Cl

Fourier absorption spectra of HCl and HF measured at room temperature and low pressures were found to show evidence of pressure-induced shifts of the spectral lines at gas pressures of only 10 torr. Self-induced shifts were measured for the HF 2-0 band and for the H³⁵Cl and H³⁷ 2-0 bands. There were also measured in the same spectra shifts in the HF 2-0 band due to HCl and shifts in both HCl bands due to HF, with indications of shift oscillation due to near-resonant dipole-dipole interactions between HCl and HF. Separate measurements were made of pressure-induced shifts in the HF 1-0 and 2-0 bands and in both isotopic HCl bands, using separately argon, neon, nitrogen and carbon dioxide as the perturbing gases.     

On the electronic spectrum of the TCNQ chains with 1/4-filled bands

Energy spectrum of one-quarter-filled one-dimensional chain with rigid and regular lattice is studied in the Hubbard model within an unrestricted Hartree-Fock approximation. The existence of an energy gap in the electronic excitation spectrum is discussed.     

Absolute frequency measurements of the 0002-0000, 2001-0000, and 1201-0000 bands of N2O by heterodyne spectroscopy

The absolute frequencies of 39 lines in the 00⁰2-00⁰0, 20⁰1-00⁰0, and 12⁰1-00⁰0 bands of N₂O in the range 4300–4800 cm^?1 have been measured by heterodyne frequency techniques. The lines were each measured in Doppler-limited absorption, with a color-center laser as a tunable probe of the N₂O and two stabilized CO₂ lasers as reference frequencies. New rovibrational constants have been fitted to these measurements. Tables of calculated transition frequencies are given, with estimated absolute uncertainties as small as 10^?4 cm^?1. The pressure shifts of four lines have been measured, and the values fall within the range of 0 to ?2 MHz/kPa (0 to ?0.2 MHz/Torr).     

The A3Π(1) ← X1Σ+ absorption spectrum of ICl: Rotational analysis of bands in the v″ = 2, 3, 4, 5 progressions (λ > 7000 Å) and a reexamination of published data for individual bands in the v″ = 0, 1, 2 progressions

Molecular constants are reported for the A³Π(1) and X¹Σ⁺ states of I³⁵Cl (0 ≤ v″ ≤ 5, 3 ≤ v′ ≤ 35) and of I³⁷Cl (v″ = 0, 11 ≤ v′ ≤ 32) from least-squares fits to individual bands. The constants are based on analyses of new bands photographed at $\text{λ > 7000}\text{A}\text{?}$ and on data previously reported in the literature. Attention is given to the choice of adequate models. The application of long-range theory to the levels of A³Π(1) near convergence indicates a homogeneous perturbation in addition to the heterogeneous perturbations established in previous work. However, there is no evidence of any discontinuities in the manifold of vibrational levels near v′ = 6 or 9 of the type suggested in previous work.     

Intensities of CH4 bands at the 4900-3700 cm-1 region

The intensities of CH₄ bands located at 3970-3700 and 4900-3970 cm^-1 were found to be 0.85±0.02 and 22.5±0.2 cm^-1/(atm-cm)_STP, respectively, by using the Wilson-Wells-Penner-Weber technique.     

Line positions and strengths of 41 bands including 10 OCS isotopologues in the 3850-4200 cm region

The present analysis substantially improves the spectroscopic characterization of near infrared OCS in a window region (3850-4200 cm⁻¹) important for atmospheric studies of Venus. Previous studies in this spectral region cataloged numerous OCS line positions, but accurate line intensities were measured for only three strong bands. In this paper, the corresponding line intensities are obtained for 41 OCS bands, including weak isotopic bands reported for the first time. The 2ν₃ (0002-0000) band is analyzed for 10 OCS isotopologues (adding ¹⁶O¹³C³⁴S, ¹⁷O¹²C³²S, ¹⁶O¹²C³⁶S, ¹⁸O¹²C³⁴S, and ¹⁶O¹³C³³S). In addition, observations of 0332-0330 of the main isotope, ¹⁶O¹²C³²S, provides accurate vibration-rotation parameters for the upper state (and the lower state, 0330 of ¹⁶O¹²C³²S). Finally, one unidentified band is seen at 3969.3 cm⁻¹; its lower state is clearly the ground state of ¹⁶O¹²C³²S. The line strengths of these seven previously unanalyzed bands plus 34 other bands of the OCS isotopologues, ¹⁶O¹²C³²S, ¹⁶O¹²C³⁴S, ¹⁶O¹³C³²S, ¹⁶O¹²C³³S, and ¹⁸O¹²C³²S, were least-squares fitted to determine strength parameters, S_v and Herman-Wallis coefficients. Finally, the intensities of 17 additional very weak bands were estimated to provide an extensive new database of OCS line parameters to support remote sensing of Venus. The integrated intensity in cm⁻¹/(molecule cm⁻²) at 296 K is 8.1×10⁻¹⁹ for the 3800-4200 cm⁻¹ region.     

The optical spectrum of the doubly charged molecular nitrogen ion: Rotational analysis of the (0-0) and (1-1) bands of the D1Σu+-X1Σg+ transition of N22+: Comparison of observations with Ab-initio calculation results

Emission spectra obtained in the 1550–1650 Å region with a 10-m vuv spectrograph are conclusively assigned to the N₂²⁺ ion. The 1589-Å band, previously observed by Carroll, and a new band of the same system, have been rotationally analyzed. Ab-initio calculations have been performed which support the assignment of these two bands to the D¹Σ_u⁺-X¹Σ_g⁺ system. The calculations also explain the observed breaking-off points in the branch structure as well as weakening and broadening of the other expected bands. These phenomena arise from electron configuration changes and perturbation effects in the ground state.     

Experimental and theoretical analysis of the 5 pnpJ =0 e , 1 e , 2 e autoionizing spectrum of Sr

The even parity 5 pnpJ = 0, 1 and 2 doubly excited autoionizing states of strontium were investigated both experimentally and theoretically. Sr atoms in an atomic beam were excited through the two-step Isolated Core Excitation (ICE) scheme 5s^{2 1} S ₀ -λ ₁ → 5 sn'p ¹ P ₁ ( n' = 12-16)-λ ₂ → [5 p _3/2 np ] _J . The final ICE transition probes the [5 p _3/2 np ] _J resonances. However, the [5 p _1/2 np ] _J series below the 5 p _1/2 threshold were excited also due to their mixing with the [5 p _3/2 np ] _J perturbers. An extended energy region was covered below and above the 5 p _1/2 ionization limit by saturating the central ICE lobe and recording as many as possible “red” and “blue” secondary lobes. J identification was achieved by using mutually parallel and perpendicular linear polarizations of the laser beams. The ICE spectra were compared to those obtained by employing a two-step excitation scheme using the bound 4 d 5 p ¹ P ₁ valence state as an intermediate one. Final identification for very complex structures was achieved after comparison with theoretical energy level positions and excitation profiles produced by the R-matrix method combined with the multichannel quantum defect theory (MQDT) method. The agreement between theoretical and observed structures is quite satisfactory. Received 31 May 2000     

High-resolution infrared spectrum of the 859- and 1711-cm−1 bands of carbonyl sulfide (OCS)

The ν₁ and 2ν₁ bands of OCS have been measured using grating spectrometers and a tunable diode laser spectrometer. Preliminary wavenumbers for OCS absorption lines useful for calibrating tunable laser systems are given for the wavenumber intervals 825 to 885 cm^?1 and 1665 to 1737 cm^?1. Measurements and an analysis are given for the bands 10⁰0-00⁰0, 11¹0-01¹0, 20⁰0-00⁰0, 21¹0-01¹0, and 30⁰0-10⁰0 of the ¹⁶O¹²C³²S isotopic species and for the 20⁰0-00⁰0 band of the ¹⁶O¹³C³²S and ¹⁶O¹²C³⁴S species. Effective band constants are given for these bands.