Infrared-microwave double-resonance spectroscopy of the ClO2 radical: A textbook example

The capability of the ir-mw double-resonance technique to produce precise spectroscopic data has been thoroughly tested in a study of the ClO₂ free radical. Although the experiments are based on fixed-frequency gas lasers, the results of the work show that rotational and vibrational information can be obtained from practically all infrared absorption bands of ClO₂ within the operating frequency range of the lasers. A wide range of microwave frequencies was searched using approximately 120 individual laser lines; double-resonance signals were observed with about 25% of the lines used. The double-resonance data obtained were sufficient to determine rotational, distortion, fine, and hyperfine constants for the vibrational states (0, 0, 0), (1, 1, 0), and (0, 0, 1) of ³⁵ClO₂ and (1, 0, 0) and (0, 0, 1) for ³⁷ClO₂. The constants for the (0, 0, 0) state of ³⁵ClO₂ and ³⁷ClO₂ and for (0, 1, 0) of ³⁵ClO₂ were refined and those for the (0, 1, 0) state of ³⁷ClO₂ were determined with data obtained from double-resonance and conventional measurements. The rotational constants obtained allowed equilibrium structures for both³⁵ClO₂ and ³⁷ClO₂ to be calculated. The structural parameters obtained in each case are in excellent agreement: $\text{r}{}_{\mathrm{e}}\text{= 1.4700(1}\text{A}\text{?}\text{)}$, θ_e = 117° 23.3′(7). The centers of the bands ν₁ and ν₁ + ν₂ ? ν₂ of ³⁵ClO₂ were precisely determined and the data available were sufficient to check the reliability of the values obtained. The band origins were also determined for ν₃, ³⁵ClO₂ and ³⁷ClO₂, and with less precision for ν₁ for ³⁷ClO₂.     

The ClO4 radical: a theoretical study on ground and excited states

In agreement with previous studies, the ground state of ClO₄ has been confirmed to be X²B₁. Vertical excitation energies and oscillator strengths were calculated by MRCI methods for doublet and quartet states of ClO₄. The highest oscillator strength was found for 1²A₁ at 2.95 eV. This state has been identified as the upper state seen by Kopitzky and co-workers in the absorption spectrum of ClO₄. Two higher states, 2²A₁ and 3²A₁, at 4.19 and 8.12 eV, respectively, also have relatively high oscillator strengths. Rydberg states start at about 9.5 eV. Geometry optimizations were performed by DFT and CCSD(T) methods. After extensive testing, the B3LYP density functional, together with the 6-311 + G(3df) basis set were chosen for calculations. Optimized geometries of seven excited states were obtained. The adiabatic excitation energy of 1²A₁ (2.40 eV) agrees closely with the observed band origin at 2.46 eV. Three excited states have one or two imaginary vibrational modes. Electron affinity and heat of formation of ClO₄ agree with literature values. None of the quartet states was found to be stable.     

Thermal and electrical properties of solid polymer electrolyte PEO9 Mg(ClO4)2 incorporating nano-porous Al2O3 filler

Solid polymer electrolyte PEO₉ Mg(ClO₄)₂ incorporating 10 wt.% nano-porous Al₂O₃ filler grains has been prepared by the solvent casting technique using acetonitrile as the common solvent. Al₂O₃ powder (activated acidic, Aldrich) with grain size 104 μm and pore size 5.8 nm were incorporated as an inert filler. Electrolyte films have been characterized by differential scanning calorimetry, complex impedance and dc polarization measurements. The nano-composite electrolyte as well as the filler-free electrolyte appear to be predominantly anionic conductors with ClO₄⁻ ions being the migrating species. The presence of the alumina filler has enhanced the ionic conductivity significantly. The conductivity enhancement has been attributed to Lewis acid–base type interactions between H groups at the filler grain surface and the ClO₄⁻ ions. Transient H-bonding through these interactions is expected to provide additional hopping sites and favourable conducting pathways for migrating ionic species.     

Subterahertz electrodynamics of (TMTSF)2X (X = ClO4, PF6) salts

The terahertz-subterahertz spectra of the complex permittivity and dynamic conductivity of polycrystalline (TMTSF)₂ClO₄ and (TMTSF)₂PF₆ samples are measured quantitatively. The spectra of (TMTSF)₂ClO₄ have absorption lines at frequencies of 7 and 30 cm^?1. The obtained temperature dependences of the line parameters in the range 5–300 K cast some doubt on the earlier concept of their phonon origin. An excitation is detected at temperatures below 20 K in the frequency range near 30 cm^?1, and its nature is related to the activation of a transverse acoustic phonon caused by the folding of the Brillouin zone due to the ordering of noncentrosymmetrical anions below 20 K. An increase in the carrier relaxation rate is found in this temperature range, which indicates a close relation between the electron and phonon subsystems in (TMTSF)₂ClO₄. Sings of additional low-energy excitations that should manifest themselves at frequencies below 1–2 cm^?1 are detected. (TMTSF)₂PF₆ containing centrosymmetrical anions has no absorption lines in the frequency range 3–20 cm^?1 and the temperature range 5–300 K.     

The microwave spectrum of cyanophosphine, H2PCN

The rotational spectra of cyanophosphine, H₂PCN, have been measured between 10 and 42.5 GHz by Fourier transform microwave spectroscopy. The rotational constants, centrifugal distortion constants, the ¹⁴N quadrupole coupling constant, and the nuclear spin-rotation coupling constants of ³¹P have been determined. Density functional ab initio calculations were performed, and the calculated values of the molecular constants are in excellent agreement with our experimentally determined results. The spectra of three isotopomers were measured, H₂P¹²C¹⁴N, H₂P¹³C¹⁴N, and H₂P¹²C¹⁵N. The derived r₀ structure is quite comparable to the ab initio predicted H₂PCN equilibrium geometry.     

EPR studies of phase transitions in perchlorates [M 2+(ClO4)2 · 6H2O] at high pressures

The EPR spectra of the Mn²⁺ ion in crystals of the perchlorate hexahydrates Zn(ClO₄)₂ · 6H₂O, Mg(ClO₄)₂ · 6H₂O, and Cd(ClO₄)₂ · 6H₂O were studied in the temperature range 77–320 K under hydrostatic pressure. It is shown that the octahedron of six molecules H₂O surrounding this paramagnetic ion is contracted along the c axis and that pressure decreases this distortion. The second-order phase transition that occurs near 200 K in the perchlorates and in other crystal hydrates is shown to be associated with changes in the bonds in the nearest ligand environment. As the pressure is increased, the phase-transition temperatures shift and the perchlorate crystals tend to a single-phase state. The low-temperature phase is assumed to disappear as the pressure increases, and this phase exists in a closed T-P region in the phase diagram. As the pressure increases, the character of the high-temperature transition in the Cd(ClO₄)₂ · 6H₂O changes: the jumplike transition at T ₁ with a 1-K hysteresis changes into a smooth transition and then disappears as the pressure increases further.     

2-三氟甲基吡啶的转动光谱及分子结构研究

本文测定了2-三氟甲基吡啶在2∽20 GHz频率范围内的高分辨转动光谱. 测定了转动常数、¹⁴N核四极耦合常数及离心畸变常数等一系列光谱参数. 同时还在自然丰度下测定了5个¹³C和1个¹⁴N单取代同位素异数体的光谱数据. 实验结果结合从头算准确地推导出2-三氟甲基吡啶的骨架结构. 实验测得同位素异数体的平面转动惯量P_cc数值均为44.46 u?²,表明此分子具有C_s对称性. 此外,本文计算了吡啶、2-氟吡啶、2-甲基吡啶和2-三氟甲基吡啶的分子表面静电势,以此分析了三氟甲基的取代对电子分布的影响.     

The microwave spectrum,harmonic force field,and structure of difluorodichloromethane

Very large numbers of rotational transitions have been accurately measured for ¹²CF₂³⁵Cl₂, ¹²CF₂³⁵Cl³⁷Cl, and ¹³CF₂³⁵Cl₂, and have been analyzed for rotational constants and quartic centrifugal distortion constants. The distortion constants have been combined with vibrational wavenumbers (both from the literature and from the present work), and with ab initio force constants also evaluated in the present work, to give an approximate harmonic force field. The rotational constants and force field have been used to evaluate ground state effective, substitution, and ground state average structures for the molecule.     

Raman light scattering,infrared absorption and DSC studies of the phase transition and vibrational and reorientational dynamics of H2O ligands and ClO4– anions in [Ba(H2O)3](ClO4)2

[Ba(H₂O)₃](ClO₄)₂ between 90 and 300 K possesses two solid phases. One phase transition of the first‐order type at: = 211.3 K (on heating) and = 204.6 K (on cooling) was determined by differential scanning calorimetry. The entropy change value (ΔS ≈ 15 Jmol^–1 K^–1), associated with the observed phase transition, indicates a moderate degree of molecular dynamical disorder. Both, vibrational and reorientational motions of H₂O ligands and ClO₄^– anions, in the high‐temperature and low‐temperature phases, were investigated by Fourier transform far‐infrared and middle‐infrared and Raman light scattering spectroscopies. The temperature dependences of the full‐width at half‐maximum values of the bands associated with ρ_w(H₂O) mode, in both infrared (~570 cm^–1) and Raman light scattering (~535 cm^–1) spectra, suggest that the observed phase transition is not associated with a sudden change of a speed of the H₂O reorientational motions. Ligands reorient fast, with correlation time of the order of several picoseconds, with a mean activation energy value E_a = 5.1 kJ mol^–1 in both high and low temperature phases. On the other hand, measurements of temperature dependences of full‐width at half‐maximum values of the infrared band at ~460 cm^–1, associated with δ_d(OClO)E mode, and Raman band at ~1105 cm^–1, associated with ν_as(ClO)F₂ mode, revealed the existence of a fast ClO₄^– reorientation in phase I and in phase II, with the E_a(I) and E_a(II) values equal to 8.0 and 6.5 kJ mol^–1, respectively. These reorientational motions of ClO₄^– are slightly distorted at the T_C. Fourier transform far‐infrared and middle‐infrared spectra with decreasing of temperature indicated characteristic changes at the vicinity of PT at T_C, which suggested lowering of the crystal structure symmetry. All these experimental facts suggest that the discovered phase transition is associated with small change of H₂O ligands and somewhat major change of ClO₄^– anions reorientational dynamics, and with insignificant change of the crystal structure, too. Copyright © 2012 John Wiley & Sons, Ltd.     

Analysis of the nuclear quadrupole interaction of Disulfur Dichloride, S2Cl2

Pure rotational spectra of S₂³⁵Cl₂ and S₂³⁵Cl³⁷Cl have been observed using a Fourier-transform microwave spectrometer. An analysis of the hyperfine structure made by considering the nuclear spin statistics showed that S₂Cl₂ has C₂symmetry, where the hyperfine splittings due to the two Cl nuclei were analyzed precisely. The nuclear quadrupole coupling constants including the off-diagonal (χ_ab, χ_ac, χ_bc) components and the nuclear spin–rotation interaction constants associated with the two Cl nuclei have been determined for the first time. We have shown that the nuclear quadrupole interaction plays an important role in the ortho–para mixing.     

The vacuum ultraviolet absorption spectrum of ClO

The flash photolysis of ClO₂ has yielded a new absorption spectrum of ClO in the vacuum ultraviolet. Six electronic transitions have been assigned and vibrational constants for the upper states are given. All of the transitions are Rydberg in nature. The first four of these transitions are thought to be ²Σ ← X²Π_i from which a spin-orbit coupling constant A = ?318 ± 5 cm^?1 is obtained for the ground state.Hot bands in three of the above systems of ClO have been observed in absorption. This has enabled the direct measurement of the ground state vibrational constant ($\text{Δ}\text{G}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{″ = 845 ± 4}\text{cm}{}^{\mathrm{?1}}$; ω_e″ = 859 cm^?1) for the first time.Extinction coefficients for a number of the ClO transitions have been measured.     

The microwave spectrum and structure of chloryl fluoride

The microwave spectra of three isotopic species of chloryl fluoride, FClO₂, in its ground vibrational state, have been measured in the frequency region 8–37 GHz. The spectra have yielded values for the rotational constants, centrifugal distortion constants, and chlorine nuclear quadrupole coupling constants, as well as the molecular dipole moment, 1.722 ± 0.03 D. The molecule has been shown to have C_s symmetry, and a pyramidal configuration, with the chlorine atom at the apex of the pyramid. The following internuclear parameters were obtained:r(Cl?F)1.697±0.003 A r(Cl?F)=1.418±0.002AThe structural parameters, quadrupole coupling constants, dipole moment and force field are explained in terms of a bonding scheme in which a fluorine 2p atomic orbital overlaps with the highest occupied orbital of ClO₂; there is considerable evidence for withdrawal of electron density from this singly occupied antibonding orbital of ClO₂ toward the fluorine atom.     

The 2v 2, v 1 and v 3 bands of H2 16O

The 2v ₂, v ₁ and v ₃ bands of H₂ ¹⁶O occurring in the region 2930–4255 cm^-1 were studied from a spectrum recorded with a high resolution Fourier transform spectrometer (resolution: 0·005 cm^-1). The set of the observed transitions leads by a least squares method to the determination of very accurate values of the rotational levels belonging to the vibrational states (000), (020), (100), (001). From these levels, using Watson's Hamiltonian, we have obtained respectively 21 and 17 rotational constants for the states (000) and (020).     

Microwave spectra of the Cl and Cl isotopomers of dichloromethylene: Nuclear quadrupole-, spin-rotation-, and nuclear shielding constants from the hyperfine structures of rotational lines

The rotational spectra of the isotopomers C³⁵Cl³⁷Cl and C³⁷Cl₂ of dichloromethylene in the ground vibronic state were recorded in the range 10-33 GHz using a molecular beam Fourier transform microwave spectrometer. CCl₂ was generated by flash pyrolysis using different precursors. The observed spectra were analyzed to yield rotational and centrifugal distortion constants, as well as the complete Cl nuclear quadrupole coupling tensors and the spin-rotation interaction constants from the hyperfine structure of the rotational lines. With inclusion of data from previous work on the most abundant species C³⁵Cl₂ [N. Hansen, H. Mäder, F. Temps, Phys. Chem. Chem. Phys. (3) (2001) 50-55.] a refined r₀ structure was determined. The spin-rotation interaction constants of all three isotopomers were used to derive ³⁵Cl and ³⁷Cl principal inertial axis nuclear magnetic shielding components which have not yet been determined by NMR spectroscopy.     

Centrifugal distortion analysis of pure rotational spectra of H216O,H217O,and H218O

Centrifugal distortion analyses based entirely on high-quality infrared data are carried out for the ground vibrational states of H₂¹⁶O, H₂¹⁷O, and H₂¹⁸O. As a result of the analyses, the values of 27 rotation and distortion constants for each species are determined. By using these constants it was possible to improve considerably the accuracy of the literature values for rotational energy levels at high J_τ, especially for H₂¹⁷O and H₂¹⁸O. The experimental values for the energy levels are deduced from the observed rotational transitions constituting the fitted data.     

The rotational a-type sepctra of 15N-labeled diazirine,H2CN2

The rotational a-type spectra of isotopically enriched diazirine isotopomers, H₂¹²C¹⁴N¹⁵N and H₂¹²C¹⁵N₂, have been recorded in the region between 8 and 300 GHZ; the latter isotopomer has been observed for the first time. Using Watson's A-reduced Hamiltonian, the rotational constants and the quartic and some sextic centrifugal distortion constants have been determined for the ground vibrational states.     

The millimeterwave spectrum of germyl fluoride: Determination and comparison of the effective, substitution, and equilibrium structures

The ground state rotational spectrum of germyl fluoride was measured up to 1273 GHz (J ≤ 63). The rotational constants and quartic and sextic centrifugal distortion constants have been determined accurately for five isotopic species in natural abundance (^{70/72/73/74/76}Ge). The high accuracy of the rotational constants of these five isotopomers allowed us to study the mass dependence of the substitution coordinate of Ge. Equilibrium rotational constants of ⁷⁴GeH₃F were deduced with the help of the axial rotational constant and the rotation-vibration interaction constants determined by high resolution infrared spectroscopy. The r₀, r_,I, and r_e structures of GeH₃F were determined.     

The submillimeter-wave spectrum and spectroscopic constants of SO2 in the ground state

The submillimeter-wave spectrum of SO₂ has been recorded with 0.004 cm^?1 resolution in the region 8–90 cm^?1. About 2000 lines were observed, 1500 of which have been assigned to the ground state rotational transitions of ³²SO₂. Molecular constants up to the 10th order have been derived, combining our data with the available microwave data in the literature. SO₂ rotational spectrum line positions up to 90 cm^?1 can be reproduced from these constants, within the experimental accuracy (2 × 10^?4 cm^?1).     

Microwave spectrum and molecular force field of tetratomic C2v molecules: NO2Cl

The rotational constants and quartic centrifugal distortion constants for NO₂³⁵Cl and NO₂³⁷Cl have been determined from an analysis of rotational transitions in the microwave and millimeter wave regions between 8.2–40 and 90–120 GHz, respectively.The values of the in-plane force constants in the general harmonic potential field have been obtained by combination of infrared and microwave data. Vibrational frequencies of ¹⁴NO₂Cl and ¹⁵NO₂Cl, inertia defects of NO₂³⁵Cl in the excited vibrational states v₃ = 1 and v₅ = 1, and first-order centrifugal distortion constants of NO₂³⁷Cl are the experimental data used in the least-squares fitting determination of force constants.     

NMR observation of a high temperature phase transition in the organic superconductor (TMTSF)2ClO4

A high temperature phase transitional behavior in the organic superconductor (TMTSF)₂ClO₄ (tetramethyltetrafulvalenium-perchlorate) was manifest in our ¹H NMR measurements. Our observations are discussed in the light of a dimensional crossover of the electronic transport.