The Lamb-dip spectrum of the J = 1 ← 0 transition of DF: Crossing resonances and hyperfine components

The Lamb-dip technique has been applied to the observation of the J = 1 ← 0 transition of DF: for the first time, the hyperfine structure due to D and F have been resolved by using microwave spectroscopy. The high accuracy of this technique allows us to provide hyperfine parameters that are in very good agreement with those obtained from molecular beam experiment. In addition, our frequencies together with the unresolved ones up to J″ value of 47 allow us to provide the most accurate ground state rotational constants of DF known at the moment. Furthermore, due to the presence of a relevant number of strong crossing resonances, the J = 1 ← 0 transition of DF can be considered an illustrative case to show how they modify the shape of Lamb-dip spectra.     

The magnetic hyperfine structure in the rotational spectrum of H2CNH

The hyperfine structure in the ground-state rotational spectrum of methanimine was studied in the frequency range of 64-172 GHz by means of the Lamb-dip technique. This allowed to resolve, in some hyperfine components due to the ¹⁴N nucleus, doublets separated by only some tenth of kHz. We explain the splittings as due to magnetic interactions of the three protons with their molecular environment. The analysis of the experimental spectrum has been guided by quantum-chemical calculations of the hyperfine parameters.     

Sub-Doppler and Doppler spectroscopy of DCN isotopomers in the terahertz region: ground and first excited bending states (v1v2v3)=(0 1 0)

The rotational spectra of the deuterium cyanide isotopic species DCN, D¹³CN, DC¹⁵N, and D¹³C¹⁵N were recorded in the vibrational ground and first excited bending state (v₂=1) up to 2 THz. The R-branch transitions from J=3←2 to J=13←12 were measured with sub-Doppler resolution. These very high resolution (∼70 kHz) and precise (±3-10 kHz) saturation dip measurements allowed for resolving the underlying hyperfine structure due to the ¹⁴N nucleus in DCN and D¹³CN for transitions as high as J=10←9. Additional high JR-branch (J=25←24 to J=28←27) transitions around 2 THz and direct l-type (ΔJ=0, J=19 to J=25) transitions from 66 to 118 GHz were recorded in Doppler-limited resolution. For the ground state of D¹³C¹⁵N, the J=1←0 transition was measured for the first time. The transition frequency accuracies for the other deuterated species were significantly improved. These new experimental data, together with the available infrared rovibrational data and previously measured direct l-type transitions, were subjected to a global least squares analysis for each isotopomer. This yielded precise sets of molecular constants for the ground and first excited vibrational states, including the nuclear quadrupole and magnetic spin-rotation coupling constants of the ¹⁴N nucleus for DCN and D¹³CN. The hyperfine structure due to the D, ¹³C, and ¹⁵N nuclei have not been resolved, but led to a broadening of the observed saturation dips.     

Vibrational and rotational analyses of bands between 636 and 660 nm in the red system of CuCl2

The long wavelength end of the electronic spectrum of CuCl₂, between 636 and 660 nm, has been recorded in the gas phase by laser-excitation spectroscopy using a sample prepared at low temperatures (ca. 10 K) in a free-jet expansion. Under these conditions, it is possible to resolve vibrational, rotational, and even Cu hyperfine structure. The (0, 0) band of the E²Π_u-X²Π_g transition has been identified with an origin at 15546.286(3) cm⁻¹ for ⁶³Cu³⁵Cl₂. The observation and analysis of bands involving vibrationally excited levels has allowed the determination of all three vibrational intervals for the E²Π_u state (ν₁ = 335.88 cm⁻¹, ν₂ = 112.42 cm⁻¹, and ν₃ = 482.17 cm⁻¹, ⁶³Cu³⁵Cl₂). In addition, two other, unrelated transitions have been identified in the same narrow wavelength region. This, combined with the observation of local perturbations of the rotational structure in various bands, reveals the presence of other closely lying electronic states in the same energy region.     

Rotational levels of the (0 0 0) and (0 1 0) states of D2O from hot emission spectra in the 320-860 cm region

The far-infrared emission spectra of deuterated water vapour were measured at different temperatures (1370, 1520, and 1950 K) in the range 320-860 cm⁻¹ at a resolution of 0.0055 cm⁻¹. The measurements were performed in an alumina cell with an effective length of hot gas of about 50 cm. More than 1150 new measured lines for the D₂¹⁶O molecule corresponding to transitions between highly excited rotational levels of the (0 0 0) and (0 1 0) vibrational states are reported. These new lines correspond to rotational states with higher values of the rotational quantum numbers compared to previously published determinations: J_max=26 and for the (0 0 0) ← (0 0 0) band, J_max=25 and for the (0 1 0) ← (0 1 0) band, and J_max=26 and for the (0 1 0) ← (0 0 0) band. The estimated accuracy of the measured line positions is 0.0005 cm⁻¹. To our knowledge no experimentally measured rotational transitions for D₂¹⁶O within an excited vibrational state have been available in the literature so far. An extended set of experimental rotational energy levels for (0 0 0) and (0 1 0) vibration states including all previously available data has been determined. For the data reduction we used the generating function model. The root mean square (RMS) deviation between observed and calculated values is 0.0012 cm⁻¹ for 692 rotational levels of the (0 0 0) state and 0.0010 cm⁻¹ for 639 rotational levels of the (0 1 0) vibrational state. A comparison of the observed energy levels with the best available values from the literature and with the global predictions from molecular electronic potential energy surface [J. Chem. Phys. 106 (1997) 4618] for the (0 0 0) and (0 1 0) states is discussed.     

The rotational spectrum of BiO radical in its X1Π1/2 and X2Π3/2 states

Rotational spectra have been observed for BiO produced in a DC discharge through a low pressure mixture of O₂, Ar, and Bi vapor. Because of the highly non-thermal distribution of states, it has been possible to observe spectra arising from the X₁²Π_1/2 level up to v = 9 and for the X₂²Π_3/2 level up to v = 5 near 10 538 cm⁻¹. Precise rotational and hyperfine parameters have been determined for the observed states. By using available near infrared (NIR) data in a merged fit, the 0-0 and 1-1 fine structure intervals have been more precisely determined. Although the quality of the fit is very good, the interpretation of the hyperfine constants is complicated by relativistic effects and the interaction of the X₂ state with A₁⁴Π_3/2 state. The magnetic and quadrupole coupling constants will be compared with those of the Bi atom and related molecules.     

The Lamb-dip spectrum of the J + 1 ← J (J = 0, 1, 3-8) transitions of HCN: The nuclear hyperfine structure due to H, C, and N

The pure rotational J + 1 ← J transitions, with J = 0, 1, 3-8, of H¹³CN have been observed in the millimeter- and submillimeter-wave region using the Lamb-dip technique to resolve the hyperfine structure due to H, ¹³C, and ¹⁴N. The present observations allow us to provide for the first time the spin-rotation constant of ¹³C and the spin-spin interaction constant S₁₂ (between H and ¹³C) as well as to remarkably improve the quadrupole coupling and spin-rotation constants of ¹⁴N. In addition, a good empirical estimation of C_I(H), based on ab initio calculations, has also been provided. Furthermore, our frequencies together with previous data permit to determine the most accurate ground state rotational parameters known up to now.     

High resolution analysis of the rotational levels of the (0 0 0), (0 1 0), (1 0 0), (0 0 1), (0 2 0), (1 1 0) and (0 1 1) vibrational states of SO2

A high resolution (0.0018 cm⁻¹) Fourier transform instrument has been used to record the spectrum of an enriched ³⁴S (95.3%) sample of sulfur dioxide. A thorough analysis of the ν₂, 2ν₂ − ν₂, ν₁, ν₁ + ν₂ − ν₂, ν₃, ν₂ + ν₃ − ν₂, ν₁ + ν₂ and ν₂ + ν₃ bands has been carried out leading to a large set of assigned lines. From these lines ground state combination differences were obtained and fit together with the existing microwave, millimeter, and terahertz rotational lines. An improved set of ground state rotational constants were obtained. Next, the upper state rotational levels were fit. For the (0 1 0), (1 1 0) and (0 1 1) states, a simple Watson-type Hamiltonian sufficed. However, it was necessary to include explicitly interacting terms in the Hamiltonian matrix in order to fit the rotational levels of the (0 2 0), (1 0 0) and (1 0 1) states to within their experimental accuracy. More explicitly, it was necessary to use a ΔK = 2 term to model the Fermi interaction between the (0 2 0) and (1 0 0) levels and a ΔK = 3 term to model the Coriolis interaction between the (1 0 0) and (0 0 1) levels. Precise Hamiltonian constants were derived for the (0 0 0), (0 1 0), (1 0 0), (0 0 1), (0 2 0), (1 1 0) and (0 1 1) vibrational states.     

SO2: High-resolution analysis of the (0 3 0), (1 0 1), (1 1 1), (0 0 2) and (2 0 1) vibrational states; determination of equilibrium rotational constants for sulfur dioxide and anharmonic vibrational constants

High resolution Fourier transform spectra of a sample of sulfur dioxide, enriched in ³⁴S (95.3%). were completely analyzed leading to a large set of assigned lines. The experimental levels derived from this set of transitions were fit to within their experimental uncertainties using Watson-type Hamiltonians. Precise band centers, rotational and centrifugal distortion constants were determined. The following band centers in cm⁻¹ were obtained: ν₀(3ν₂)=1538.720198(11), ν₀(ν₁ + ν₃)=2475.828004(29), ν₀(ν₁ + ν₂ + ν₃)=2982.118600(20), ν₀(2ν₃)=2679.800919(35), and ν₀(2ν₁ + ν₃)=3598.773915(38). The rotational constants obtained in this work have been fit together with the rotational constants of lower-lying vibrational states [W.J. Lafferty, J.-M. Flaud, R.L. Sams, EL Hadjiabib, J. Mol. Spectrosc. 252 (2008) 72-76] to obtain equilibrium constants as well as vibration-rotation constants. These equilibrium constants have been fit together with those of ³²S¹⁶O₂ [J.-M. Flaud, W.J. Lafferty, J. Mol. Spectrosc. 16 (1993) 396-402] leading to an improved equilibrium structure. Finally the observed band centers have been fit to obtain anharmonic rotational constants.     

Fine and hyperfine structure in the atomic spectrum of niobium

A parametric analysis of the fine and the magnetic dipole hyperfine structure for the three configurations of odd parity 4d³5s5p, 4d⁴5p and 4d²5s²5p was performed. Effective one-electron parameters were determined and theoretical predictions are given for the magnetic dipole hyperfine structure constants A for the levels of these three configurations. Additionally, 12 new energy levels could be found, four of odd and eight of even parity, by re-analysing data for experimental wavelengths of Nb.     

Lineshape analysis of the J = 3 ← 2 and J = 5 ← 4 rotational transitions of room temperature CO broadened by N2, O2, CO2 and noble gases

Collisional relaxation has been considered for millimeter lines of carbon monoxide at room temperature. Accurate measurements of carbon dioxide- and rare gases-broadened widths have been performed on the J = 3 ← 2 rotational line of ¹²CO by using a video-type spectrometer. Measurements of nitrogen-, oxygen-, and xenon-broadened widths of the J = 5 ← 4 rotational line of ¹³CO were also carried by using a frequency-modulated spectrometer. A lineshape study performed on all the investigated binary systems provide confirmation that Voigt profile is not a suitable model to analyse experimental lines in the millimeter-waves region. On one hand, using this profile in the low pressure range, i.e. in the Doppler regime, the retrieved collisional linewidths do not follow a linear variation with the perturbing gas pressure. On the other hand, regardless of the pressure, lineshapes exhibit a narrowed profile. An accurate analysis of the pressure dependence of relaxation rates show that the Galatry profile is not appropriate and that experimental lineshapes are actually Speed Dependent Voigt profiles. Accurate broadening parameters were retrieved from this profile and compared to previous reported values and predictions calculated from the Robert-Bonamy formalism. Finally a variation of the ratio of relaxation speed dependence to broadening parameters versus relative masses of the collision partners is presented.     

Widely usable interpolation formulae for hyperfine splittings in the 127I2 spectrum

Based on new systematic high precision measurements of hyperfine splittings in different rovibrational bands of ¹²⁷I₂ in the near infrared spectral range between 778 nm and 816 nm, and the data in the range from 660 nm to 514 nm available from literature, the quantum number dependence of the different hyperfine interaction parameters was reinvestigated. As detailed as possible parameters were re-fitted from the reported hyperfine splittings in literature, considering that the interaction parameters should vary smoothly with the vibrational and rotational quantum numbers, and follow appropriate physical models. This type of consistency has not been sufficiently taken into account by other authors. To our knowledge it is now possible for the first time to separate the hfs contributions of the two electronic states B ³ and X ¹ Σ ⁺ _g for optical transitions in a very large wavelength range. New interpolation formulae could be derived for both states, describing the quantum number dependences of the nuclear electric quadrupole, of the nuclear spin-rotation and also of the nuclear spin-spin interactions. Using these new interpolation formulae the hyperfine splittings for the components with the quantum number condition F - J = 0 can be calculated with an uncertainty of ≤30 kHz for transitions in the wavelength range between 514 nm and 820 nm. Received 17 July 2001 and Received in final form 17 October 2001     

The continuum absorption in H2O+N2 mixtures in the 2000-3250 cm spectral region at temperatures from 326 to 363 K

The absorption spectra of H₂O+N₂ mixtures, as well, as the spectra of pure gases, have been measured using a Fourier-transform infrared spectrometer at a resolution of 0.1 cm⁻¹. The sample temperatures were 326, 339, 352, and 363 K. Water vapor pressures varied from 8 (60 torr) to 34.5 kPa (259 torr). The nitrogen pressure was kept constant at about 414 kPa (4.1 atm). The path length was 100 m. The continuum absorption coefficients obtained in the spectral range 2000-3250 cm⁻¹ (3.1-5 μm) do not depend significantly on temperature, as is predicted by the well known MT_CKD model. But there are significant deviations in the continuum spectral behavior and magnitude. Around 2050 cm⁻¹ the measured absorption coefficients C_f are about two times larger than those of the model. This deviation grows rapidly at shorter wave lengths, reaching a maximum of two orders of magnitude in the middle of the window at 2500 cm⁻¹. At this point, the deviation starts to decrease significantly and around 3100 cm⁻¹ our results are in agreement with the MT_CKD model. This behavior of the deviation is due to the broad and structureless feature in the region of the nitrogen fundamental band. Most likely, this feature is the N₂ fundamental band component, induced by collisions between H₂O and N₂ molecules. The data obtained and a comparison with the results from the other available sources are presented.     

Microwave study of the rotational spectrum of oxygen molecule in the range up to 1.12 THz

Microwave study of the rotational transitions of oxygen molecule in its electronic and vibrational ground states is reported. Eight transitions belonging to N=3-1, N=5-3, and N=7-5 groups were investigated. Central line frequencies and pressure broadening parameters for O₂ and N₂ as perturbers were determined. The highest frequency of measured transition (N,J)=(7,6)-(5,6) has been 1.12 THz. Spectrometer with backward wave oscillator (BWO) and acoustic detector (RAD) was used. Since this experiment has more than doubled the number of previously measured rotational lines of oxygen molecule and better accuracy was achieved, the fitting of new set of rotational transition frequencies has been performed and new more accurate molecular constants for in , v=0 state have been obtained.     

Accurate rotational spectroscopy of sulfur dioxide, SO2, in its ground vibrational and first excited bending states, v2 = 0, 1, up to 2 THz

Approximately 150 pure rotational transitions each have been recorded for SO₂, v₂ = 0 and 1, in selected frequency regions up to 2 THz. The J and K_a quantum numbers reach very high values: 92 and 23, respectively, for the ground vibrational state and 81 and 21, respectively, for the first excited bending state. The highest levels accessed are almost 3000 cm⁻¹ above ground. The relative experimental uncertainties Δν/ν are about 10⁻⁸ for several medium to strong, isolated lines, and generally better than 2.5 × 10⁻⁷. Improved spectroscopic parameters have been obtained for both states, particularly for the excited bending state. In fact, the accuracies with which the energy levels of the v₂ = 1 state are known depend essentially only on the accuracy with which the vibrational spacing is known from infrared spectroscopy.     

High resolution Fourier transform spectrum of HDO in the 7500-8200 cm region: revisited

The HDO absorption FT spectrum is recorded and analyzed in the 7500-8200 cm⁻¹ spectral region. The high accuracy ab initio calculation of Schwenke and Partridge was successfully applied for spectrum assignment that resulted in derivation of 508 precise rovibrational energy levels for the (3 0 0), (0 3 1), (1 1 1), (0 6 0), (2 2 0), and (0 0 2) states, with 295 of them being reported for the first time. In particular, eight new energy levels, including the band center at 7914.3170 cm⁻¹, were derived for the highly excited bending (0 6 0) state from transitions borrowing their intensities through local high-order resonance coupling with the (3 0 0) and (0 3 1) states.     

High-resolution Fourier transform spectrum of H2S in the region of 8500-8900 cm

High-resolution Fourier transform infrared spectrum of H₂S was recorded and analyzed in the region of the polyad. More than 450 transitions were assigned to the 3ν₁ + ν₂ and 2ν₁ + ν₂ + ν₃ bands with the maximum values of quantum numbers J and K_a equal to 14, 7, and 14, 9 for these two bands, respectively. The theoretical analysis was fulfilled with the Hamiltonian which takes into account strong resonance interactions among the studied vibrational states (3 1 0), (2 1 1), and also “dark” states (0 3 2) and (2 3 0). The rms deviation is 0.0019 cm⁻¹. The intensity borrowing effect in the doublets in the P-branch transitions of the 3ν₁ + ν₂ and 2ν₁ + ν₂ + ν₃ bands is observed and discussed.     

Formation of linear structures of Sr and Gd films on the Mo(1 1 2) and W(1 1 2) surfaces

At low coverages, alkaline earth and rare earth layers adsorbed on furrowed transition metal surfaces--such as W(1 1 2) and Mo(1 1 2)--tend to form commensurate linear structures built of monoatomic chains directed across the furrows. Presented Monte Carlo simulations provide insight into parameters of the long-range indirect interaction that, in competition with a dipole-dipole interaction, leads to formation of the linear structures. The most impressive result of the simulations is the revealed repulsive effective interaction between adjacent atoms in linear Sr chains on W(1 1 2) surface. In this case, formation of the linear chains is accomplished due to pronounced minima in the potential of indirect interaction along the surface furrows. This result predicts that a single Sr chain cannot exist on the W(1 1 2) surface.     

On the study of high-resolution rovibrational spectrum of H2S in the region of 7300-7900 cm

High-resolution Fourier transform infrared spectrum of H₂S was recorded and analyzed in the region of the v=v₁+v₂/2+v₃=3 poliad. Experimental transitions were assigned to the 3ν₁, 2ν₁+ν₃, ν₁+2ν₃, 3ν₃, 2ν₁+2ν₂, and ν₁+2ν₂+ν₃ bands with the maximum value of quantum number J equal to 11, 14, 10, 11, 8, and 11, respectively. The theoretical analysis was fulfilled with the Hamiltonian model which takes into account numerous resonance interactions between all the mentioned vibrational states. The rms deviation of the reproduction of 510 upper energy levels (derived from more than 1550 transitions) with 75 parameters was 0.0022 cm⁻¹.