Shock-tube determination of absorption cross sections and A2Δ − X2Π band transition moments of SiH

The overall absorption cross sections and electronic transition moments of the A²Δ ? X²Π band system of SiH have been determined by using an absorption technique with a shock tube at temperatures of 2600–3800 K over the wavelengths of 150–650 nm. Absorption cross sections are shown to be dominated by continua. The possible contributions to the overall cross sections by a low-lying ⁴Σ^- and a high-lying ⁴Σ^- state are discussed. At 200, 228, 340, 405, and 550 nm, the continuum cross sections are (2.9±1.0)×10^-17, (2.0±0.5)×10^-17, (3.2±0.6)×10^-18, (3.8±0.6)×10^-18, and (1.8±0.8)×^-18cm², respectively. The overall emission intensity and the Si+H→SiH+hv radiative recombination rate are (6.7± 2.3)×10^-35(3500/T)^0.7(Si)(H) watt-cm^-3 and (1.3±0.4)×10^-17(3500/T)^1.1(Si)(H) cm^-3-s^-1, respectively. The A ? X transition moments are 0.12±0.04a.u. for the (0, 0) and (1, 1) bands. The intensity of each branch in the A ? X (0, 0) band follows approximately the prediction based on the Hönl-London factors of Kovacs. The data are applied to the study of the flow field around a spacecraft entering the Jovian atmosphere.     

Measurement at different temperatures of absolute intensities,line half-widths,and broadening by Ar and N2 for the 3001II←0000 band of CO2

Absolute intensities, self-broadening coefficients, and foreign-gas broadening by Ar and N₂ were measured at temperatures of 197, 233 and 294 K for the 30⁰1_II←00⁰0 band of CO₂ at 6348 cm^-1. Also, the intensity parameters and total band intensity were calculated. We obtained for the vibration-rotation interaction factor the value F(m) = 1 + (0.26 ± 0.06) × 10^-2m + (0.92 ±0.32 × 10^-4 m²; for the purely vibrational transition moment, we found ¦R₀₀₀₀^3001_II¦к(0.4351 ± 0.0014)()10^b3 debye; and, for the total band intensity at STP conditions, S_band(30⁰1_II←00⁰0)_STP = 1255 ± 9 cm^-1 km^-1 atm^-1.Self-broadening coefficients at 197 and 294 K were also measured, as well as broadening by Ar and N₂. Foreign-gas-broadening efficiencies (Ar and N₂) were determined. Finally, a comparison is made with measurements by other authors and with theoretically calculated values.     

Tunable laser study of the ν10 + ν11 band of cyclopropane

Diode laser measurements of the ν₁₀ + ν₁₁ (l_tot = ±2) perpendicular band of cyclopropane have led to the assignments of roughly 600 lines in the 1880–1920-cm^?1 region. Most of the spectra were recorded and stored in digital form using a rapid-scan mode of operating the laser. These spectra were calibrated, with the aid of a computer, by reference to the R lines of the ν₁ + ν₂ band of N₂O. The ground state constants we obtained are (in cm^?1) B = 0.670240 ± 2.4 × 10^?5, D_J = (1.090 ± 0.054) × 10^?6, D_JK = (?1.29 ± 0.19) × 10^?6, D_K = (0.2 ± 1.1) × 10^?6. The excited state levels are perturbed at large J values, presumably by Coriolis couplings between the active E′(l_tot = ±2) and the inactive A′(l_tot = 0) states. Effective values for the excited state constants were obtained by considering only the J < 15 levels. The A₁-A₂ splittings in the K′ = 1 excited states were observed to vary as q_effJ(J + 1), with q_eff = (2.17 ± 0.17) × 10^?4 cm^?1.     

High-resolution infrared spectrum of the ν2 + ν3 band of 14N16O2

The ν₂ + ν₃ band of ¹⁴N¹⁶O₂ has been recorded with resolution of 0.028 cm^?1. Ground state and upper state rotational constants have been obtained. The band center obtained, ν₀ = 2355.1517 ± 0.0011 cm^?1 (error cited is 3σ), has been combined with the band centers recently determined for ν₃ and ν₂ to calculate X₂₃ = ?11.348 ± 0.020 cm^?1 where the uncertainty cited is based on reasonable estimates of the absolute frequency error.     

Quenching of excited strontium atomic state measured in H2- and CO-flames

The efficiency of resonance fluorescence, Y, of the strontium resonance line (¹P₁→¹S₀ transition) at 4607.33 Å was measured in CO/N₂O, CO/O₂/Ar, and H₂/O₂/CO₂/N₂ flames at atmospheric pressure. From these data, the specific quenching cross sections, σ_qu, for CO₂ and CO were found to be (60 ± 10) Ų and  (300 ± 60) Ų, respectively. The experimental cross sections were confronted with the intermediate ionic-state curve-crossing model and chemical quenching model, respectively.     

Spectral intensities of the 4-μm ν1 + ν3 combination band of SO2

The transition intensities of the 4-μm bands of SO₂ are measured with high precision using a tunable laser difference-frequency spectrometer. The band strength calculated from the ν₁ + ν₃ combination band data at 295.2K is S_v⁰ = 10.54 ± 0.04 cm^?2 atm^?1. Here the uncertainty (three standard deviations) quoted is for the relative precision only; the absolute accuracy, which depends on the sample pressure calibration, is ～1%. F-factors and “hot” band results are also obtained.     

Ferroelectric and optical properties of Ba6Ti2Nb8O30 single crystals

The dielectric, optical and non-linear optical properties of Ba₆Ti₂Nb₈O₃₀ single crystals were examined from room temperature up to the Curie temperature of 245°C. The spontaneous polarization at room temperature was estimated as 0·22±0·01 C/m². The linear electrooptic constants were measured as r₃₃^T=(1·17±0·02)×10^?10 and r₁₃^T=(0·42±0·01)×10^?10 m/V. The non-linear optical coefficients were d₃₃=(15·1±2·0)×10^?12 and d₃₁=(11·0±2·0)×10^?12 m/V, which are comparable to those of Ba₄Na₂Nb₁₀O₃₀. Temperature dependences of δ₃₃ and δ₃₁ (Miller's δ) were found to be proportional to that of P_s.     

Chemisorption of H2 on W(100): Absolute sticking probability,coverage, and electron stimulated desorption

Measurements of both the absolute sticking probability near normal incidence and the coverage of H₂ adsorbed on W(100) at ~ 300K have been made using a precision gas dosing system; a known fraction of the molecules entering the vacuum chamber struck the sample crystal before reaching a mass spectrometer detector. The initial sticking probability S₀ for H₂/W(100) is 0.51 ± 0.03; the hydrogen coverage extrapolated to S = 0 is 2.0 × 10¹⁵ atoms cm^?2. The initial sticking probability S₀ for D₂/W(100) is 0.57 ± 0.03; the isotope effect for sticking probability is smaller than previously reported. Electron stimulated desorption (ESD) studies reveal that the low coverage β₂ hydrogen state on W(100) yields H⁺ ions upon bombardment by 100 eV electrons; the ion desorption cross section is ~ 1.8 × 10^?23 cm². The H⁺ ion cross section at saturation hydrogen coverage when the β₁ state is fully populated is ? 10^?25 cm². An isotope effect in electron stimulated desorption of H⁺ and D⁺ has been found. The H⁺ ion yield is ? 100 × greater than the D⁺ ion yield, in agreement with theory.     

The absorption spectrum of CO2 around 7740 cm-1

Absolute intensities of the vibration-rotation lines of the CO₂ 401_II←000 band 7734 cm^-1 are measured under high-resolution, low-pressure conditions by use of a White-type 25-m base-path, absorption cell together with a 5-m Czerny-Turner spectrometer. The total band intensity S_B, the purely vibrational transition moment

, and the vibration-rotation interaction constant ζ are calculated from the intensity measurements. The values obtained for these parameters are S_B(401_II) = (7.06±0.07) × 10^-5 cm^-2 atm^-1_293°K,

= (3.08±0.03)×10^-5 debye, and ζ = (2.5±0.5)×10^-4. The intensity of the associated “hot band” 411_II←010 is also determined and found to be S_B(411_II←010) = (0.53±0.02)×10^-5 cm^-2 atm^-1_293°K.     

Electronic-excitation transfer collisions in flames—V. Cross sections for quenching and doublet-mixing of K(42P)-doublet by N2, O2, H2 and H2O

Weighted average cross sections for quenching of the K(4²P)-doublet by N₂, H₂, O₂ and H₂O, measured in flames, show no significant temperature dependence in the range from 1500 to 2500K. Doublet mixing cross sections for K(4²P$\text{3}\text{2}$?4²P$\text{1}\text{2}$) transitions were measured at 1720K for N₂, O₂, H₂O. The ratios of both mixing cross sections were measured independently and were found to agree with the detailed balance condition within 2 per cent. It is shown that an ionic intermediate-state model cannot explain the large magnitude of N_2? mixing cross sections.     

Determination of the radiative lifetime of the d3Πg state of the C2 molecule by the laser-pyrolysis technique. A feasibility study

The feasibility is studied of using the laser-pyrolysis technique for determination of the radiative lifetimes of molecules.Measurements of time-resolved spectral emission were made on spatially resolved sections of the luminous plume produced by laser illumination of a graphite target in a vacuum. The nature of certain emission continua was investigated. The effects on C₂ Swan band emission of focal spot size, illumination power density, height and width of the plasma section observed and its distance from the target were studied. Conditions were determined for measuring physically significant radiative lifetimes for the d³Π_g, v=0 and v=1 levels, of C₂. In particular, the laser flux used was 3.8×10⁸W-cm^?2 while observations were made of a plume section from 0.5 to 0.7 mm from the target. The results, τ(0,0)=235±20 ns, τ(0,1)=250±20 ns, τ(1,0)=255±20 ns, are compared with those obtained by other methods. They are in good agreement with results obtained by pulsed electron excitation. Analysis of the experimental conditions in previous experiments using the laser-pyrolysis technique for measuring τ(d³Π_g of C₂ shows that they could not have lead to meaningful results of purely molecular properties.     

High accurate peak positions for calibration purposes with the lowest fundamental bands ν2 of N2O and CO2

The lowest fundamental vibration rotation bands ν₂ of nitrous oxide (N₂O) and carbon dioxide (CO₂) have been measured with a Fourier transform spectrometer at the resolution of 0.001 cm⁻¹. The spectra have been calibrated with the high accurate peak positions of the carbonyl sulfide (OCS) ν₂ band, which has been recently produced as a candidate for a secondary standard by calibrating first the 2ν₂ band with the CO₂ laser bands around 10 μm and then transferring the calibration to ν₂ with the internal energy levels of OCS. In the present work the OCS ν₂ and ν₁ bands were measured together with the spectra of N₂O and CO₂. Then the OCS ν₁ band was measured by calibrating it with the 2ν₂ band of OCS. The linearity of the wavenumber scale was checked by comparing the corresponding line positions in the OCS ν₁ band in these two separate measurements. The absolute accuracy of the ν₂ band centers of N₂O and CO₂ were evaluated to be 6.8 × 10⁻⁶ and 8.4 × 10⁻⁶ cm⁻¹, respectively.     

Magnetostriction measurements of CoS2 single crystal

The magnetorestriction constants of CoS₂ single crystal were measured by a capacitance method in a temperature range from liquid N₂ to the Curie temperatures.The constants γ₁₀₀ and γ₁₁₁ are ?1.9 × 10^?6 and 5.7 × 10^?6 at liquid N₂ temperature respectively, and the absolute values of the constants decrease monotonically with the increase of the temperature. The volume magnetorestriction constant δω/δH at 110 K in the ferromagnetic state is 6 × 10^?10 Oe^?1.     

Measurements of the electronic transition moment of the A2Π−X2Π system of ClO

The electronic transition moment of the A²Π?X²Π band system of ClO has been determined from spectral emission measurements behind incident shock waves in Cl₂-O₂ mixtures. The temperature of the radiating gas was typically 3500°K. Narrow bandpass radiometers were used to obtain absolute measurements of the ClO emission from which electronic transition moments were derived by a synthetic spectrum analysis. Absolute measurements of the O₂ Schumann-Runge system and the photo-dissociation cross section of ClO are also reported.     

Collisional broadening of nitrous oxide transition lines in the ν1 + 2ν2 band by noble gases

A tunable diode laser is used to measure the foreign gas broadening for several rotational states in the R branch of the 12⁰0-00⁰0 vibration-rotation band of N₂O. The results indicate that rotational relaxation is the chief pressure broadening mechanism. The resulting cross sections for He and Ne turn out to be almost independent of the rotational quantum number. Ar and Kr, however, show a clear dependency. This seems to contradict the results of the infinite order sudden approximation.     

Magnon Raman scattering in CoBr2

The one-magnon Raman spectrum of CoBr₂ has been investigated as a function of temperature, and peak frequency, integrated intensity and width parameters obtained. The results obtained for the band energy at low temperature (22.2 ± 0.2 cm^-1 at 5.7.K) are in good agreement with AFMR and neutron scattering results. The one-magnon energy renormalises relatively slowly with increasing temperature and is about 15 cm^-1 at T_N = 19 K, whereas the integrated intensity approaches zero like the magnetization at T_N and the width diverges. A low intensity band at 26.8 ± 1 cm^-1 (7.6K) may be due to two-magnon scattering from spin waves along the c-axis.     

Diode laser line strength measurements of the (ν4 + ν5)0 band of 12C2H2

A diode laser spectrometer that was operated in sweep integration mode was used to measure individual line strengths for 17 R-branch transitions of the (ν₄ + ν₅)⁰ combination band of ¹²C₂H₂ at 7.4 μm. Analysis of these results gives a band strength S_v = 64.4 ± 2.0 cm^?2 atm^?1 at 296 K. Line-broadening parameters for several of these transitions were determined by using both N₂ and He as broadening gases.     

Specific heat of NaNO2 near its transition points

Using an a.c. technique, the specific heat of NaNO₂ was measured as a function of temperature near its antiferroelectric-to-paraelectric phase transition point (T_N). The transition was found to be of the second order. The critical exponents are; α = 0·38 for ? = 2 × 10^?4 ～ 1 × 10^?1, and α′ = 0·18 for ? = ?2 × 10^?4 ～ ?3 × 10^?3. The critical exponents deduced from the scaling-law relations are roughly close to the values obtained from a random phase approximation for a system with an isotropic interaction. However, a difference was recognized between the observed exponent for the specific heat and the values theoretically given for T > T_N by the random phase approximation for a system with a short-range interaction or for a system with a long-range dipolar interaction. A thermodynamical analysis was made by using the generalized Pippard relation, and the present result was found to be consistent with the pressure dependence of the antiferroelectric transition point.     

Absolute intensity measurements of the CO2 bands 401III←000 and 411III←010

The absolute intensities of the transitions 401_III←000 and 411_III←010 of CO₂ have been measured from spectra obtained under high resolution. Both the vibration-rotation line intensities and the integrated band intensities are reported. The rotationless transition moment of 401_III←000 is deduced and a vibration-rotation interaction factor F(m) = 1+(4.92×10^?4)m+(4.4×10^?7)m² is determined. The values obtained are: S_Band(401_III←000) = (25.54±0.22)×10^?5 cm^?2atm_{(293 K)}^?1, |R₀₀₀^401_III| = (1.87±0.02)×10^?4D, and S_Band(411_III←010) = (1.83±0.13)×10^?5 cm^?2atm_{(293 K)}^?1.     

Investigation of the absorptions of monoisotopic OsO4 with CO2 and N2O laser lines with saturation spectroscopy

Some absorption features of monoisotopic ^{186–190,192}OsO₄ have been studied by saturated absorption using low-pressure CO₂ and N₂O lasers. Ground-state absorptions of the ν₃ fundamental band were distinguished from hot-band absorptions by investigation of the linear absorption coefficients, and were assigned on the basis of frequency calculations. In addition the vibrational transition moment was evaluated. A few lines were found, which, due to their unusual saturation properties, were identified as forbidden transitions arising from off-diagonal terms of a sixth rank tensor in the effective Hamiltonian. Their observation permits a value of the tensor centrifugal distortion constant to be derived: D_t = (2.045 ± 0.018) × 10^-9 cm^-1.