Integral intensities of absorption bands of silicon tetrafluoride in the gas phase and cryogenic solutions: Experiment and calculation

The spectral characteristics of the SiF₄ molecule in the range 3100–700 cm^?1, including the absorption range of the band ν₃, are studied in the gas phase at P = 0.4–7 bar and in solutions in liquefied Ar and Kr. In the cryogenic solutions, the relative intensities of the vibrational bands, including the bands of the isotopically substituted molecules, are determined. The absorption coefficients of the combination bands 2ν₃, ν₃ + ν₁, ν₃ + ν₄, and 3ν₄ are measured in the solution in Kr. In the gas phase of the one-component system at an elevated pressure of SiF₄, the integrated absorption coefficient of the absorption band ν₃ of the ²⁸SiF₄ molecule was measured to be A(ν₃) = 700 ± 30 km/mol. Within the limits of experimental error, this absorption coefficient is consistent with estimates obtained from independent measurements and virtually coincides with the coefficient A(ν₃) = 691 km/mol calculated in this study by the quantum-chemical method MP2(full) with the basis set cc-pVQZ.     

Infrared spectrum of formaldehyde: Coriolis interactions in the combination bands ν2 + ν6 and ν2 + ν3

A high-resolution infrared spectrum of H₂CO was measured in the range from 2600 to 3300 cm^?1. Vibration-rotation lines assigned to the combination bands ν₂ + ν₃ (a-type) and ν₂ + ν₆ (b-type) were analyzed as asymmetric-rotor bands by taking account of the Coriolis interactions among the ν₂ + ν₃, ν₂ + ν₆, and ν₂ + ν₄ states, though none of the ν₂ + ν₄ band lines have yet been definitely identified. The main results in cm^?1 units (with 2.5 times standard errors in the last digits given in parentheses) are: ν₀ = 3238.45(1), A - B?= 8.252(3), B?= 1.2053(2), and B - C = 0.1719 (assumed) for ν₂ + ν₃; ν₀ = 3000.10(1), A - B?= 8.125(46), B?= 1.2075(5), and B - C = 0.1693(14) for ν₂ + ν₆; and ν₀ = 2904.6(48), A - B?= 8.225(54), B?= 1.2023(20), and B - C = 0.1522 (assumed) for ν₂ + ν₄; the effective Coriolis interaction terms are: ξ_26,24^a = 10.10(3)cm^?1 and ξ_23,26^c = 0.96(3)cm^?1 under the assumption that ξ_23,24^b = 1.2841cm^?1. A second combination band 2ν₂ + ν₆ measured with lower resolution gave ν₀ = 4734.81(6)cm^?1.     

The infrared spectrum of C3O2: The interaction between ν7 and the ν2 and ν4 vibrations

The 3ν¹₇, 3ν³₇, and 4ν⁰₇ hot bands of the ν₄ fundamental of C₃O₂ in the 1580 cm^?1 region were analyzed from tunable diode laser spectra and the ground state to ν₄ + 2ν⁰₇ band at 1644 cm^?1 from Fourier transform spectra (FTS). The molecular constants for all of the v₄ 1 ← 0 bands as well as the intensity of the ν₀ + 2ν⁰₇ sum band relative to the ν₄ fundamental were in agreement with the predictions of the model of Weber and Ford. FTS spectra at 0.05 cm^?1 resolution were obtained of the sum and difference bands of ν₂ with ν₇ in the 750–900 cm^?1 region. Sharp Q branches occur for each ν₇ state in the sum bands, but only a number of R-branch bandheads and no recognizable Q branches in the difference bands. Assignments of the sum band Q branches through v₇ = 6 were made and molecular constants were determined for the ν₂ + ν¹₇ ← 0 transition at 819.7 cm^?1. The ν₇ potential function in the v₂ = 1 state was found to have a 1.2 cm^?1 barrier with a minimum at α = 4.9°, where 2α is the angular deviation from linearity. The Q-branch positions predicted from the calculated energy levels fit those observed within several cm^?1.     

Manifestation of resonance dipole-dipole interaction in spectra of low-temperature molecular mixtures of C2F6 in CF4 and CF4 in C2F6

We have measured IR absorption spectra of solutions C₂F₆ in CF₄ (T = 178 K) and CF₄ in C₂F₆ (T = 173 K) in the overtone range of the spectrum. We have studied how the resonance dipole-dipole interaction affects the formation of contours of bands that correspond to transitions to states involving the vibrations ν₁₀(C₂F₆) and ν₃(CF₄), which are strong in the dipole absorption. For the system C₂F₆ in liquid CF₄, the state ν₂ + ν₁₀(C₂F₆) resonantly interacts with the state ν₂(C₂F₆) + ν₃(CF₄), and, for the system CF₄ in liquid C₂F₆, the state ν₁ + ν₃(CF₄) resonantly interacts with the state ν₁(CF₄) + ν₁₀(C₂F₆). The contours of the bands ν₂ + ν₁₀ (C₂F₆) in the spectrum of the mixture with CF₄ and of the bands ν₁ + ν₃(CF₄) in the spectrum of the mixture with C₂F₆ have been calculated.     

The Hot Bands of Methane between 5 and 10 μm

Experimental line intensities of 1727 transitions arising from nine hot bands in the pentad–dyad system of methane are fitted to first and second order using the effective dipole moment expansion in the polyad scheme. The observed bands are ν₃− ν₂, ν₃− ν₄, ν₁− ν₂, ν₁− ν₄, 2ν₄− ν₄, ν₂+ ν₄− ν₂, ν₂+ ν₄− ν₄, 2ν₂− ν₂, and 2ν₂− ν₄, and the intensities are obtained from long-path spectra recorded with the Fourier transform spectrometer located at Kitt Peak National Observatory. For the second order model, some of the 27 intensity parameters are not linearly independent, and so two methods (extrapolation and effective parameters) are proposed to model the intensities of the hot bands. In order to obtain stable values for three of these parameters, 1206 dyad (ν₄, ν₂) intensities are refitted simultaneously with the hot band lines. The simultaneous fits to first and second order lead to rms values respectively of 21.5% and 5.0% for the 1727 hot band lines and 6.5% and 3.0% for the 1206 dyad lines. The band intensities of all 10 pentad–dyad hot bands are predicted in units of cm⁻²atm⁻¹at 296 K to range from 0.931 (for 2ν₄− ν₄) to 7.67 × 10⁻⁵(for 2ν₄− ν₂). The total intensities are also estimated to first order for two other hot band systems (octad–pentad and tetradecad–octad) that give rise to weak transitions between 5 and 10 μm.     

On the Study of Resonance Interactions and Splittings in the PH3 Molecule: ν1, ν3, ν2+ν4, and 2ν4 Bands

The high-resolution (0.005 cm⁻¹) Fourier transform infrared spectrum of PH₃ is recorded and analyzed in the region of the fundamental stretching bands, ν₁ and ν₃. The ν₂+ν₄ and 2ν₄ bands are taken into account also. Experimental transitions are assigned to the ν₁, ν₃, ν₂+ν₄, and 2ν₄ bands with the maximum value of quantum number J equal to 15, 15, 13, and 15, respectively. a₁-a₂ splittings are observed and described up to the value of quantum number K equal to 10. The analysis of a₁/a₂ splittings is fulfilled with a Hamiltonian model which takes into account numerous resonance interactions among all the upper vibrational states.     

High resolution infrared spectrum of the ν4 band of DCCF

The bending vibration-rotation band ν₄ of DCCF was studied. The measurements were carried out with a Fourier spectrometer at a resolution of about 0.03 cm^?1. The constants B₀=0.29141(1)cm^?1, α₄=?5.02(2)×10^?4cm^?1, q₄=4.52(3)×10^?4cm^?1, and D₀=9.2(4)×10^?8cm^?1 were derived. The rotational analysis of the “hot” bands 2ν₄(Δ) ← ν₄(II) and 2ν₄(Σ⁺) ← ν₄(II) was performed. In addition, the “hot” bands ν₄ + ν₅ ← ν₅ were assigned. A set of vibrational constants involved was derived.     

Calculations of ozone line shifting induced by N2 and O2 pressure

Ozone line shifts by nitrogen and oxygen pressure are computed for the ν₁ + ν₃, 2ν₁ and 2ν₃ bands of the 5 μm spectral region by a semiempirical approach. The calculated values agree with measurements better than 0.001 cm^?1 atm^?1 for 98% of O₃–N₂ lines and 87% of O₃–O₂ lines. In contrast with the water molecule case, the polarization components of the interaction potential are shown to contribute to the line shift more efficiently than the electrostatic interactions. As intermediate results, the mean dipole polarizability and the components of the polarizability tensor for the vibrational states (101), (200), and (002) of ozone molecule are determined by least-squares fitting of theoretical shifts to some experimental values. The temperature exponents for the ν₁ + ν₃ band lines are also estimated.     

Infrared spectra of thin films of α-crystalline hexafluoroethane: a manifestation of resonant dipole–dipole interaction in the range of fundamental vibrational modes ν<Subscript>5</Subscript> and ν<Subscript>10</Subscript>

Infrared reflection-absorption spectra of thin films of α-crystalline hexafluoroethane deposited on a gold-plated copper mirror are measured at temperatures of 70 and 80 K. The bands corresponding to strong in the dipole absorption vibrations ν₅ and ν₁₀ have complex contours, the shape of which is explained in terms of the resonant dipole–dipole interaction between identical spectrally active molecules of the crystal. Splittings of the complex ν5 and ν10 bands are explained taking into account two effects: the Davydov splitting and the LO–TO splitting of the strong modes. Bands of the asymmetric ¹³С¹²СF₆ isotopologue in the absorption spectrum of the crystal exhibit an anomalously large isotope shift as compared with the shift in the spectrum of free molecules. This anomaly is explained by intermolecular resonant dipole–dipole interaction of asymmetric ¹³С¹²СF₆ isotopologue with molecules of the environment, consisting of the most abundant ¹²C₂F₆ isotopologue. The correctness of the given interpretation is confirmed calculating these three effects in the model of resonant dipole–dipole interaction.     

Tunable laser diode study of the ν3 band of SiF4 near 9.7 μm

Doppler-limited tunable-diode laser spectra of the stretching fundamental ν₃ of ²⁸SiF₄ near 1031 cm^?1 were analyzed and the spectroscopic constants determined. The ν₃ vibrational dipole moment derivative was determined for several rovibrational lines.     

Absorption intensities for vibration-rotation bands and the dipole-moment expansion of HBr

Line intensities in the four 0–2, 0–3, 0–4, 0–5 vibration-rotation bands of HBr were measured. The electric dipole matrix elements 〈0|M|ν'〉 for vibrational transitions with ν'?5 have been calculated by using a Dunham potential and the analytical solution of the Schrödinger equation described by R.H. Tipping. A dipole-moment expansion accurate to M₅ was determined by fitting these matrix elements to the available experimental data on line intensities. The experimental results were also used to calculate the Einstein coefficients of the R₀ lines for the bands ν' → ν′' with ? ν' ? 5.     

Measurements and calculations of Ar-broadening parameters of water vapour transitions in a wide spectral region

The water vapour line-broadening (γ) and shift (δ) coefficients for 310 lines of 10 vibrational bands ν₁, ν₃, 2ν₂, ν₁+ ν₂, ν₂+ ν_3, 2ν₂ +ν₃, 2ν₁, ν₁+ ν₃, 2ν₃ and ν₁ +2ν₂ induced by argon pressure were measured with a Bruker IFS HR 125 spectrometer. The measurements were performed at room temperature, at the spectral resolution of 0.01 cm^–1 and over a wide pressure range of Ar. The calculations of the broadening coefficients γ and δ were performed in the framework of the semi-classical method. The intermolecular potential was taken as the sum of the atom–atom potential and the vibrationally and rotationally dependent isotropic induction+dispersion potential. The measured γ and δ were combined with literature data for the ν₂ and 3ν₁+ν₃, 2ν₁+2ν₂+ν₃ vibrational bands, and the optimal sets of potential parameters that gave the best agreement with the measured broadening coefficients for each vibrational band separately were found. Then, combined experimental data of 13 vibrational bands of H₂O perturbed by Ar were used to determine the analytical dependence of some potential parameters on vibrational quantum numbers.     

The ν1, ν2, and ν3 Band Systems of 3-Isocyano-2-propynenitrile (NCCCNC): Comparison with the ν4 System of Dicyanoacetylene

The hot bands in the ν₁, ν₂, and ν₃ band systems of NC-CC-NC (3-isocyano-2-propynenitrile) have been investigated and transitions from nv₉-levels with n up to 4 have been identified. Two weak bands have also been observed in the gas phase infrared spectrum at 2157 and 2410 cm⁻¹, of which the latter is probably 2v₄. A preliminary investigation of some analogous hot bands in the v₄ band system of the related molecule NC-CC-CN (dicyanoacetylene) is also reported.     

Microwave spectroscopic study of the SiF radical

The microwave spectrum of the SiF radical was observed in both ${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and ${}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ of the ground vibronic state. The SiF radical was produced by a dc discharge either in a $\text{SiF}{}_4\text{SiH}{}_4$ mixture or in a transient molecule SiF₂ generated by the reaction of SiF₄ with heated solid silicon. The latter gave twice as intense a spectrum. A least-squares fit to the observed spectrum showed the rotational constant and the centrifugal distortion constant to be 17 350.2752(63) and 0.03188(13) MHz, respectively, with three standard errors in parentheses applying to the last digits of the constants. The lambda-doubling parameter p₀ was found to be negative, ?87.67 MHz, indicating that the ²Σ⁺ excited state contributions dominate over those of ²Σ^?. All four hyperfine coupling constants a, b, c, and d were determined and were employed to discuss the unpaired-electron spin and orbital distributions in the SiF radical.     

Half-lives of the Tz=1/2 series nuclei, 81Zr and 85Mo

Excited states with spin larger than 5 were newly established in the ¹³²Cs nucleus via the ¹²⁴Sn(¹¹B,3n) reaction. Rotational bands built on the νh_11/2 ? πd_5/2, νh_11/2 ? πg_7/2 and νh_11/2 ? πh_11/2 configurations were observed up to spin I ～ 16. The νh_11/2 ? πh_11/2 band shows inverted signature splitting below I < 14. A dipole band was firstly observed in doubly odd Cs nuclei.     

Intracavity spectroscopy of high-temperature water vapor in the region of 1.06 μm

The absorption spectrum of water vapor is studied in the region of 9375–9460 cm^?1 and at temperatures within 300–1200 K using an intracavity laser spectrometer based on a Nd laser having a threshold absorption sensitivity of 10^?8 cm^?1. More than 270 absorption lines are detected in the high-temperature spectrum of water vapor, 70% of which are assigned to ten vibrational bands: 3ν₂ + ν₃, 2ν₁ + ν₂, ν₁ + ν₂ + ν₃, ν₂ + 2ν₃, ν₁ + 3ν₂, 3ν₃ ? ν₂, 2ν₂ + 2ν₃ ? ν₂, ν₁ + 2ν₂ + ν₃ ? ν₂, 2ν₁ + ν₃ ? ν₂, and ν₂ + 3ν₃ ? 2ν₂. The vibrational-rotational energy levels are determined.     

Study of the Fundamental Bands of GeD4 by High-Resolution Raman and Infrared Spectroscopy: First Experimental Determination of the Equilibrium Bond Length of Germane

The four fundamental bands of ⁷⁰GeD₄ have been analyzed using the STDS software developed in Dijon (http://www.u-bourgogne.fr/LPUB/sTDS.html). Both infrared and Raman spectra were used to observe all fundamental bands. Infrared spectra of monoisotopic ⁷⁰GeD₄ were recorded in the regions 600 and 1500 cm⁻¹ using the Bruker 120HR interferometer at Wuppertal. The resolution (1/maximum optical path difference) was between 2.3 and 3.3×10⁻³ cm⁻¹ for the ν₃ and ν₄ infrared-active fundamental bands as well as for the interacting ν₂ band. A high-resolution stimulated Raman spectrum of the ν₁ band has been recorded in Madrid. The instrumental resolution of the Raman spectrum was 3.3×10⁻³ cm⁻¹. We have performed a global fit of the ground state, ν₂/ν₄ bending dyad, and ν₁/ν₃ stretching dyad. We have used 1146, 139, and 676 assigned lines for ν₂/ν₄, ν₁, and ν₃, respectively. The standard deviation is 2.2×10⁻³ cm⁻¹ for the bending dyad, 1.6×10⁻³ cm⁻¹ for the ν₃ infrared lines, and 1.7×10⁻³ cm⁻¹ for the ν₁ Raman lines. These results enabled us to perform the first experimental determination of the equilibrium bond length of germane as r_e=1.5173(1) Å.     

An IR spectroscopic study of liquid ozone and ozone dissolved in liquid argon

We have measured and interpreted the IR spectra of liquid ozone films at 78–85 K and ozone dissolved in liquid argon at 91–95 K. A less hindered rotation of ozone molecules in argon manifests itself as an intensity redistribution, caused by the Coriolis interaction, from the states ν₃(B ₁) and ν₁ + ν₃(B ₁) to the states ν₁(A ₁) and 2ν₁(A ₁), respectively. The occurrence of wings in the contours of the bands ν₁(A ₁), 2ν₁(A ₁), and 2ν₃(A ₁) in liquid Ar and their absence in the spectrum of O₃ also confirms the conclusion that the rotational motion of ozone molecules in an inert solvent at low temperatures is relatively less hindered. Maxima of ozone bands in Ar solution are shifted toward lower frequencies compared to those in the gas phase by 1–30 cm^?1, which corresponds to the following shifts of harmonic frequencies of the molecule: Δω₁ = ?1.85(5) cm^?1, Δω₂ = ?0.67(7) cm^?1, Δω₃=?7.20(5) cm^?1. It was found that the absorption band of the ν₃ mode in the spectrum of O₃ in the liquid phase has a complicated asymmetric contour because of the resonance dipole-dipole interaction. The first and second spectral moments of this band have been determined to be M ₁ = 1030.6 cm^?1 and M ² = 240.0 cm^?2.     

Investigation of the temperature dependence for the spectra of supercooled water in the middle infrared

The temperature dependence of the bending ν₂, combination ν₂ + ν _L , and stretching (ν₁, ν₃, 2ν₂) absorption bands in the infrared spectra of supercooled water with a temperature-change step Δt from 2 to 2.5°C was studied using an advanced infrared Fourier spectrometer. It was found that the frequency of the maximum of the stretching absorption band (2700–3700 cm^?1) decreases with the reduction of the water temperature from ?0.5 to ?5.0°C. The frequency of the maximum of the combination absorption band (2130 cm^?1) increases with the reduction of the water temperature in a range from ?3.0 to ?5.0°C. The frequency of the maximum of the absorption band of bending oscillation (1640 cm^?1) is invariable with a reduction of the water temperature from ?0.5 to ?5.0°C.     

Studying the Concentration Dependences of IR Spectra for Aqueous Solutions of Alkali Metal Chlorides at a Negative Temperature

In this work, the concentration dependences of IR spectra were studied for aqueous LiCl, NaCl, RbCl, and CsCl solutions within the range from 4 to 0.2 M and an aqueous KCl solution within the range from 3 to 0.2 M at a temperature of –3.5°C in the middle IR region. The wavenumbers of the absorption band maxima were determined for stretching (ν₁, ν₃), combined (ν₂ + ν_L), and bending ν₂ vibrations at these concentrations. The established trends of the shift in the considered absorption bands provided a basis to make several conclusions about the structural transformations of the studied solutions with a decrease in concentration within the studied range. The calculations demonstrated an increase in the energy of hydrogen bonds between water molecules and their reduction in length with decreasing concentration for all of the studied solutions.