High resolution FTIR study of the ν5 and ν6 bands of CH2D35Cl: analysis of resonances and determination of ground and upper state constants

The isotopically pure form of methyl chloride, CH₂D³⁵Cl, was synthesized and investigated by Fourier transform infrared spectroscopy with an unapodized resolution of 0.004?cm^?1 in the range 650–900?cm^?1, the region of the lowest fundamentals ν₅ (827?cm^?1) and ν₆ (714?cm^?1). These distinct bands have been analysed in detail in the P-, Q- and R-branches. In spite of their expected a/b-hybrid nature, both envelopes show the peculiar characteristic of only a-type bands of near prolate asymmetric top molecules. Ground state parameters have been determined for the first time through ground state combination differences from both bands. Parameters of the excited vibrational states and coupling constants have been obtained using a model which accounts for c-type Coriolis interaction and ΔK_a?=?±?2 anharmonic resonance.     

First far-infrared high-resolution analysis of the ν2 and ν4 bands of phosgene 35Cl2CO and 35Cl37ClCO

ABSTRACT

A Fourier transform spectrum of phosgene (Cl₂CO) has been recorded in the 17.3-μm spectral region at a temperature of 180 K and at a resolution of 0.00102 cm^?1 using a Bruker IFS125HR spectrometer coupled to synchrotron radiation, leading to the observation of the ν₂ and ν₄ vibrational bands of the two isotopologues ³⁵Cl₂CO and ³⁵Cl³⁷ClCO. The corresponding upper-state ro-vibrational levels were fit using a Hamiltonian model accounting for the A-type Coriolis interaction linking the rotational levels of the 2¹ and 4¹ vibrational states. In this way, it was possible to reproduce the upper-state ro-vibrational levels to within the experimental uncertainty, i.e. ～0.30 × 10^?3 cm^?1. Very accurate rotational and centrifugal distortion and interaction constants were derived from the fit, together with the following band centres: ν₀(ν_2, ³⁵Cl₂CO) = 572.526299(30) cm^?1, ν₀(ν_4, ³⁵Cl₂CO) = 582.089026(30) cm^?1, ν₀(ν_2, ³⁵Cl³⁷ClCO) = 568.951791(35) cm^?1 and ν₀(ν₄, ³⁵Cl³⁷ClCO) = 581.758279(35) cm^?1.     

High-resolution analysis of the ν1 and ν5 bands of phosgene 35Cl2CO and 35Cl37ClCO

Fourier transform spectra of phosgene (Cl₂CO) have been recorded in the 11.75 and 5.47 μm spectral regions using a Bruker IFS125HR spectrometer at resolutions of 0.00102 and 0.0015 cm^?1, respectively, leading to the observation of the ν₅ and ν₁ vibrational bands of the two isotopologues ³⁵Cl₂CO and ³⁵Cl³⁷ClCO. The corresponding upper state ro-vibrational levels were fit using Watson-type Hamiltonians and/or a Hamiltonian matrix accounting for resonance effects when necessary. In this way, it was possible to reproduce the upper state ro-vibrational levels to within the experimental accuracy, i.e. ～0.17 × 10^?3 cm^?1. Very accurate rotational and centrifugal distortion constants were derived from the fit together with the following band centres: ν₀(ν_5, ³⁵Cl₂CO) = 851.012737(20) cm^?1, ν₀(ν_5, ³⁵Cl³⁷ClCO) = 849.995451(90) cm^?1, ν₀(ν_{2 +} ν_3, ³⁵Cl³⁷ClCO) = 864.42370(50) cm^?1, ν₀(ν_1, ³⁵Cl₂CO) = 1828.202514(40) cm^?1 and ν₀(ν_1, ³⁵Cl³⁷ClCO) = 1827.246444(20) cm^?1.     

Potential of the A 1Σ u + state of He2

The potential of the lowest excited singlet state of He₂ is calculated. The best function includes 209 configurations constructed from 10 σ basis orbitals. Excellent agreement with experimental quantities depending on the shape of the potential near the minimum (equilibrium interatomic separation, vibrational and rotational constants for the lower vibration levels) is obtained. The dissociation energy is 18 600 cm^-1, compared to the experimental 19 910±50 cm^-1. Agreement is not as good for the highest vibrational levels.     

Spectral Characteristics of Edge Electrostatic Turbulence in the HL-2A Tokamak

A three-tip array is used in the HL-2A tokamak to investigate the spectral characteristics of electrostatic turbulence inside the last closed flux surface （LCFS） about 5 cm. Two-point correlation techniques are used to analysis the turbulence structure. It is found that the drift wave turbulence mainly is composed of low-frequency and long wavelength wave packets. The poloidal propagation is mainly in electron-diamagnetic direction, sometimes it propagates in ion-diamagnetic direction, which is influenced by Doppler-frequency shift. The radial propagation velocity is outward and the sizeable fraction of the poloidal velocity, implying that the radial mode plays an important role in the cross field transport.     

The rotational spectrum of the SH radical in its XΣ state

All the available data on the rotational energy levels of the SH⁺ (sulfoniumylidene) radical in the v = 0 and 1 levels of the X³Σ⁻ ground state have been subjected to a single, weighted least-squares fit to determine an improved set of molecular parameters for this molecule. The results have been used to calculate the rotational spectrum of the SH⁺ radical in the v = 0 and 1 levels up to the N = 4-3 transition.     

A photoelectron spectroscopic study of the second ionisation of the CF(X2Π) radical

The CF(X²Π) radical has been re-investigated with vacuum ultraviolet photoelectron spectroscopy. Two bands were observed and assigned to the ionisations CF⁺(X¹Σ⁺)←CF(X²Π) and CF⁺(a³Π)← CF(X²Π). The first band, which has been observed previously, has an adiabatic ionisation energy of (9.11±0.02) eV and a vertical ionisation energy of (9.55±0.02) eV. For the second band, three vibrational components were observed with the first, the most intense, at an ionisation energy of (13.94±0.02) eV. Analysis of the vibrational structure in the two observed bands allowed ω_e and r_e to be determined as 1810±30 cm⁻¹ and 1.154±0.005 Å, respectively for the first ionic state, CF⁺(X¹Σ⁺), and 1614±30 cm⁻¹ and 1.213±0.005 Å, respectively for the second ionic state, CF⁺(a³Π). Comparison of the ionisation energies and spectroscopic constants obtained has been made with values obtained from recent multi-reference configuration interaction calculations.     

Estimation of hyperfine coupling constants of 29Si nuclei in the radical anions of trimethylsilyl-substituted π-electron systems

An attempt has been made to relate the coupling constant a _Si of a ²⁹Si nucleus in the radical anions of nine trimethylsilyl derivatives of π-electron systems to the spin populations ρ _Si and of the silicon and the substituted carbon centre , respectively. For the parameter Q _CSi of the relation an absolute value of circa 20 gauss is found, whereas Q _Si appears not to be significantly different from zero. The coupling constants a _Si calculated by means of this relation agree moderately well with the experimental values (standard error circa 0·6 gauss). An HMO model in which the trimethylsilyl substituents are treated as pseudo-π-centres, with the parameters h _Si = -1·5 and k _CSi = 0·55, reproduces satisfactorily the spin distribution in the corresponding radical anions.     

Low temperature vibrational relaxation of OD in the A2Σ, state

The vibrational relaxation of the A ²Σ state of OD has been studied in the low translational temperature environment of an argon free-jet (T_trans near 5 K). Using laser induced fluorescence (LIF), the absolute vibrational relaxation rate coefficients were measured for OD A²Σ (ν′) to be 7.1 ± 2.6 × 10^?11, 5.9 ± 1.4 × 10^?11, and 2.7 ± 1.1 × 10^?11 cm³ s^?1 for the ν = 3, 2 and 1 states, respectively. State-to-state relaxation rate coefficients were also obtained for the ν= 1, ? = 1 level going to ν= 0, ? levels in the A²Σ manifold. The rotational relaxation rate coefficient for ν= 1, ?= 1 in the A state of OD was found to be 9.6 ± 1.0 × 10^?11cm³s^?1. These values are consistent with values measured for OH A²Σ, and the total loss rates are near the capture rate coefficient value. The vibrational relaxation rate coefficients k_ν appear to be governed by the vibrational energy of the molecule rather then by interaction with nearby dissociative states such as the a⁴Σ state. The relative Einstein A factors for the A²σ (ν = 3) state of OD were determined and compared with the available calculated value.     

Investigations on molecular constants of the CD（X^2∏） radical and elastic collisions between ground-state C and D atoms at low temperatures

The potential energy curve of the CD(X~2Π) radical is obtained using the coupled-cluster singles-doublesapproximate-triples [CCSD(T)] theory in combination with the correlation-consistent quintuple basis set augmented with diffuse functions,aug-cc-pV5Z.The potential energy curve is fitted to the Murrell-Sorbie function,which is used to determine the spectroscopic parameters.The obtained D0,De,Re,ωe,ωeχe,αe and Be values are 3.4971 eV,3.6261 eV,0.11197 nm,2097.661 cm 1,34.6963 cm 1,0.2083 cm 1 and 7.7962 cm 1,respectively,which conform almost perfectly to the available measurements.With the potential obtained at the UCCSD(T)/aug-cc-pV5Z level of theory,a total of 24 vibrational states have been predicted for the first time when J = 0 by solving the radial Schr¨odinger equation of nuclear motion.The complete vibrational levels,the classical turning points,the inertial rotation constants and centrifugal distortion constants are reproduced from the CD(X~2Π) potential when J = 0,and are in excellent agreement with the available measurements.The total and the various partial-wave cross sections are calculated for the elastic collisions between the ground-state C and D atoms at energies from 1.0×10 11 to 1.0×10 4 a.u.when the two atoms approach each other along the CD(X~2Π) potential energy curve.Only one shape resonance is found in the total elastic cross sections,and the resonant energy is 8.36×10 6 a.u.The results show that the shape of the total elastic cross section is mainly dominated by the s partial wave at very low temperatures.Because of the weak shape resonances coming from higher partial waves,most of them are passed into oblivion by the strong total elastic cross sections.     

Simulating electron momentum spectra of iso-C2H2Cl2： A study of the core electronic structure

Electron momentum spectroscopy(EMS) has been used for the first time to study core electronic structure of isoC2H2Cl2. In the present work, the pronounced difference between ionization energies of two C1 score orbitals(2A1 and 3A1) is seen as a chemical shift of 3 eV, which is due to different chemical environments of the related carbon atoms. Both the calculated spherically averaged core electron momentum distributions(MDs) and three-dimensional electron momentum density maps show that these core molecular orbitals(MOs) 2A1and 3A1 exhibit strong atomic orbital characteristics in real and momentum space. However, the core states 2B2 and 4A1, which are almost degenerate and related to two equivalent atoms, exhibit notable differences between the momentum and position depictions. In contrast to the position space, the momentum density maps of these two core MOs highlight the interference effects which are due to the nuclear positions. The 2B2 orbital of iso-C2H2Cl2 is the antisymmetric counterpart of the 4A1 core orbital in real space. However, it relates to the 4A1 orbital by an exchange of maxima and minima in momentum space. Due to interference effects between electrons scattered from different atomic centers, modulations with a periodicity of 1.12 a.u. can be seen in the computed momentum densities, which tend to decay with increasing electron momenta. Accordingly, the EMS can not only effectively image the electronic structure of compounds by studying valence orbitals, but also provides direct information on the nature of the nuclear geometry by investigating the core states.     

Spectral–kinetic characteristics of the F2 laser transition

A theoretical model for the F₂(D–A) laser transitions is built. The model includes a scheme of the main laser transitions proposed. A value of the radiative lifetime of the upper laser level in the conventional kinetic models of the F₂ laser is proved to be underestimated by one order of magnitude. A general theory of steady-state light amplification in a molecular laser with non-equilibrium vibrational distribution is developed. Relations of the small-signal gain and the saturating energy flux with parameters of molecular electronic–vibrational kinetics are established. The theory is applied to explain properties of F₂ laser amplifiers. PACS 31.70.Hq; 42.55.Lt     

The Calibration Kit Spectral Fluorescence Standards—A Simple and Certified Tool for the Standardization of the Spectral Characteristics of Fluorescence Instruments

With the Calibration Kit Spectral Fluorescence Standards BAM-F001-BAM-F005, we developed a simple tool for the characterization of the relative spectral responsivity and the long-term stability of the emission channel of fluorescence instruments under routine measurement conditions thereby providing the basis for an improved comparability of fluorescence measurements and eventually standardization. This first set of traceable fluorescence standards, which links fluorescence measurements to the spectral radiance scale in the spectral range of 300-770 nm and has been optimized for spectrofluorometers, can be employed for different measurement geometries and can be adapted to different fluorescence techniques with proper consideration of the underlying measurement principles.     

Assignment of the Schüler band of the ammonium radical to the 3p2F2-3s2A1 electronic transition

Various visible emission bands observed by Schuster and by Schüler, Michel, and Grün when ammonia was subjected to a discharge or to electron beam excitation have been shown by Herzberg to be due to the ammonium radical, NH₄. It is proposed here that the main band of Schüler et al. near 6635 Å in NH₄ and 6750 Å in ND₄ is the 0-0 band of the electronic transition 3p²F₂-3s²A₁ of the odd electron outside the closed-shell NH₄⁺ or ND₄⁺ core, analogous to the D lines of the isoelectronic Na atom. This interpretation is consistent with recent work by Porter and co-workers on neutralized-ion-beam spectroscopy and by Hunziker and co-workers on the absorption spectrum of ND₄ by laser frequency modulation spectroscopy. The theory of the rotational structure of a p²F₂-s²A₁ electronic transition is developed. In the accompanying paper by Alberti, Huber, and Watson on the absorption spectrum of the Schüler band obtained in a flash discharge experiment, it is shown that the observed rotational structure is fully explained by this assignment. The other visible bands of the ammonium radical may represent vibrational structure of the 3p²F₂-3s²A₁ electronic transition.     

Telecommunications—the state of the art

This article is a survey of the technological foundations of telecommunications, including both point-to-point electrical communication wing wires, cables and other guiding media. and radio wave broadcasting to many receivers via terrestrial transmitters or Earth-orbiting space satellites. The characteristics of analogue and digital telecommunication signals, the means available for their transmission and switching me described, together with the organization of local distribution, national and global networks. The various services that can be provided over such networks, including in addition to telephonic communication, audio and video conferencing, data and facsimile transmission and new vied-display data/information access services (Teletext) are outlined. Finally, the sociological implications of these technological and service developments me considered, for example in terms of their impact on urban and rural planning, where people live and work, and on energy economy by reducing the need to travel.     

The high-resolution spectrum of the ν1 + ν2 band of NO2: A spin-induced perturbation in the ground state

The spectrum of the ν₁ + ν₂ band of NO₂ has been studied with a resolution of 0.025 cm⁻¹. Spin-rotation constants and rotational constants are reported. An interesting perturbation has been found in the ground state of the molecule which occurs when the K_a = 0 and K_a = 2 levels become accidentally nearly degenerate around N = 42. An explanation of this interaction is presented.