The vapor phase Raman spectra,Raman band contour analyses,Coriolis constants,force constants,and values for thermodynamic functions of the trihalides of group V

The vapor phase Raman spectra have been recorded of the molecules PX₃ (X = F, Cl, or Br), AsX₃ (X = F, Cl, Br, or I), and SbX₃ (X = Cl, Br, or I) in sealed tubes at 22–365°C as appropriate. Attempts to record the vapor phase Raman spectra of the molecules PI₃, SbF₃, and BiX₃ (X = F, Cl, Br, or I) were unsuccessful. The infrared and Raman rotational branch separations of the a₁ species fundamentals for these molecules are in agreement with the theoretically calculated values. The Raman band contours of the e-species fundamentals have been analyzed to yield, in favorable cases, values for the corresponding Coriolis constants which have been compared with those obtained from infrared band contour analyses, and which have been employed to constrain the e-species force constants. It is concluded that the Raman contour method for defining Coriolis and thus force constants should be regarded as further, but not necessarily the best, experimental method with which to help to constrain the field. Values for various thermodynamic functions of the molecules have been calculated from the new values for the fundamental frequencies and from the most recent structural data.     

The vapor-phase Raman spectra,Raman band contour analyses,Coriolis constants,and force constants of spherical-top molecules MX4 (M = Group IV element, X = F,Cl, Br,or I)

The Raman spectra of 21 tetrahalides of Group IV have been recorded in the vapor phase at temperatures between 20 and 420° C. The Raman shifts of the Q branches of each fundamental are reported. In agreement with the selection rules, the ν₁(a₁) fundamental of each molecule has no rotational structure. With two exceptions, the separation between the OP and RS branches of the ν₂(e) fundamental of each molecule has been measured and found to be in close agreement with that calculated from an extended form of the Placzek-Teller theory. Due to first-order Coriolis coupling, the OP, RS branch separations of the ν₃(t₂) and ν₄(t₂) fundamentals of each molecule are different from each other and from those of the ν₂(e) fundamental. It has been possible to determine Coriolis constants for most of the tetrahalides from these branch separations, using both a previously published procedure and also a new procedure in which analytical expressions for each subbranch are derived. There is close agreement between the zeta values so determined and the corresponding values determined from infrared band contour analyses in those cases where the latter are available. Force constants based on the fundamental frequencies and the zeta values are reported.     

The vapor phase Raman spectra,Raman band contour analyses,Coriolis coupling constants,and e-species force constants of the molecules SPF3, FCCl3, and BrCCl3

The vapor phase Raman spectra of the molecules SPF₃, FCCl₃, and BrCCl₃ have been recorded at pressures of up to 1 atm over the fundamental frequency regions. The Raman band contours of the e-species fundamentals have been analyzed to yield first-order Coriolis coupling constants from which, together with the fundamental frequencies, e-species force constants of the general harmonic potential function have been evaluated. The results for thiophosphoryltrifluoride are compared with those deduced previously on the basis of infrared band contour analyses.     

The vapour phase Raman spectra,Raman band contour analyses,Coriolis coupling constants,and e-species force constants for the molecules HCF3, ClCF3, BrCF3, and ICF3

The vapour phase Raman spectra of the molecules HCF₃, ClCF₃, BrCF₃, and ICF₃ have been recorded at pressures of up to 1 atmosphere over the fundamental frequency regions. The Raman band contours of the e-species fundamentals have been analysed to yield first-order Coriolis coupling constants from which, together with the fundamental frequencies, e-species force constants of the general harmonic potential function have been evaluated. One force field was found for fluoroform, but two different ones were found for the molecules ClCF₃, BrCF₃ and ICF₃.     

First- and second-order Coriolis interactions in symmetric top molecules: Application to the microwave spectrum of cyclopentadienyl thallium

Matrix elements are derived for both first- and second-order Coriolis interactions between A₁ and E₁ vibrational modes in symmetric tops, with particular reference to sign. The results are applied to the observed microwave transitions J → J + 1 for A₁ and E₁ states of the C_5ν molecule cyclopentadienyl thallium in various excited vibrational states. The microwave transitions in the excited A₁ states v₄ = 1, 2, 3, the excited E′ state v′₀ = 1 and the combination state v₄ = 1, v′₀ = 1 have yielded constants which are anomalous in several respects (1). Coriolis interactions between the ν₄ and ν₁₀ vibrations are shown to account for the observed anomalies.     

A critique of the term value approach to determining molecular constants from the spectra of diatomic molecules

Two alternative methods for the reduction of observed line positions to spectroscopic constants are compared. In the direct approach, the line positions are fit directly to expressions for the energy level differences in which the upper and lower state molecular constants enter as unknowns. In the traditional term value approach, a two-step procedure is followed where first a set of intermediate unknowns, the upper and lower state term values are calculated from the observed line positions and secondly these term values for each vibrational state, are fit separately to energy expressions in which the molecular constants of that state enter as unknowns. It is shown that there is correlation between the term values of all vibrational states included in the reduction. Thus, the separate fitting of term values to energy level expressions for each vibrational state does not retain this correlation and the molecular constants found in this manner cannot be the minimum-variance, linear, unbiased (MVLU) estimates and the accompanying standard deviations cannot be unbiased estimates. However, if the molecular constants of all the vibrational levels are determined simultaneously from all the term values in a correlated least-squares fit, then the molecular constants will be equal to those determined from the direct approach, i.e., the MVLU set. Furthermore, missing lines and the frequent occurrence of two independent sets of lines within a band both cause the molecular constants obtained from the traditional term value approach to differ even more from the MVLU set. Finally, the limitations of reducing groups of bands simultaneously are discussed. Certain singlet systems are given as examples of the above conclusions.     

Centrifugal distortion effects in SF2: Calculation of the force field and infrared spectrum

Measurements of the microwave spectrum of SF₂ have been extended up to J = 43 in order to account for the effects of centrifugal distortion. Seventy-five transitions have been included in a weighted least squares fit of the measured spectrum with an rms deviation of 0.078 MHz. The force field for SF₂ has been determined from the centrigufal distortion constants. The vibrational spectrum, as yet unobserved, has been predicted from the force field as have been the Coriolis coupling constants and the average structure.     

On the calculation and interpretation of centrifugal distortion constants: A statistical basis for model testing: The calculation of the force field

Watson's treatment of the theory of centrifugal distortion effects is reviewed in detail and special attention is drawn to the relationship between Watson's treatment and the Kivelson-Wilson treatment. The relationship between the distortion parameters and the force field for XYZ-type molecules is also reviewed in order to remove ambiguities and inconsistencies presently found in the literature. Finally, procedures for exploiting the statistics associated with a least-squares analysis of the data are presented as a guide for model testing and for detecting misassignments and mismeasurements. A series of examples illustrating the results of these procedures are presented using the published spectra of SO₂, OF₂, SiF₂ and NSF. In the cases of OF₂, SiF₂ and NSF, improved values for the rotational constants are obtained.     

Fourier transform infrared spectroscopy of the 2ν3 overtone band of different ICN isotopomers: an improved evaluation of the anharmonic force field of cyanogen iodide

The weak 2ν₃ overtone band of the three isotopomers of cyanogen iodide, I¹²C¹⁴N, I¹³C¹⁴N, and I¹²C¹⁵N, has been recorded in the range from 4200 to 4400 cm⁻¹ with a resolution of 0.02 cm⁻¹ using a Fourier transform infrared spectrometer. The following band origins have been determined from the analysis of the spectra: ν₀ (I¹²C¹⁴N)=4332.8368 cm⁻¹, ν₀ (I¹³C¹⁴N)=4235.7355 cm⁻¹, and ν₀ (I¹²C¹⁵N)=4274.2851 cm⁻¹. This allowed us to achieve complete knowledge of the energies for all levels of ICN corresponding to double vibrational excitation. An improved evaluation of the quartic force field of cyanogen iodide has been performed using the new data obtained together with those already known from previous works.     

On the calculation of force constants using isotopic frequencies by parametric method: Application to systems of (3×3) order

A method is proposed for the determination of angle parameters for ONF, ONCl and ONBr, utilising the isotopic frequencies of two isotopically substituted molecules. The force constants, Coriolis coupling constants, inertia defect, mean amplitudes of vibration and rotational distortion constants were also calculated and compared with literature values.     

Application of the Monte Carlo method to anharmonic force constant calculations: The anharmonic potential functions of some nonlinear symmetrical triatomic molecules

The nonuniqueness of the solution of the quartic anharmonic potential function for some symmetrical nonlinear triatomic molecules is demonstrated using the empirical potential function of Pliva and a Monte Carlo estimation technique. A modification of the method to allow for a varying harmonic force field is introduced. The results obtained indicate that the method might be used as a basis for selection of physically acceptable solutions, with a possible extension to the determination of harmonic potential constants for more complex molecules.     

Thermal and field emission effects of laser radiation on metal whisker diodes: Application to infrared detection devices

In a series of recent experiments, research groups have made absolute frequency measurements with laser beams in the infrared region of the spectrum (λ ? 10 μm) using a metal point contact diode for generation, frequency mixing and detection. It has been postulated that the mechanism for the nonlinear current-voltage characteristic of the diode is tunnelling of electrons through an intermediate oxide film from the whisker into the metal base, i.e., the configuration is considered to be a metal-oxide-metal (MOM) tunnelling junction. Several features of the diode's operation create considerable doubt concerning the applicability of the MOM tunnelling mechanism. Analysis of the available experimental data led us to postulate an alternate solid state mechanism, namely a thermally enhanced field emission process. Such emission would be a consequence of the immersion of the whisker tip in the laser radiation resulting in (1) conduction heating which induces thermionic emission and (2) generation of an electric field at the tip necessary for electron tunnelling by field emission. In this paper we calculate rigorously the power absorbed in the metal whisker from the incident radiation. From the power absorbed, the heat conduction equation is solved for model geometries to obtain the laser induced temperature distribution at the whisker surface. Estimates of the electric field are obtained and combined with temperature calculations to obtain the nonlinear I–V characteristics of the thermally enhanced field emission model. Finally some simple experiments are proposed to test the thermal field emission hypothesis as a possible mechanism to explain the nonlinear characteristics of the metal whisker point contact diode.     

On the applicability of the rigid band model to the metallic sodium tungsten bronzes: A photoemission study using synchrotron radiation

W4f, Na2p photoelectron spectra and valence band spectra are reported for a series of cubic metallic Na_xWO₃ (0.4 < x < 0.85) bronzes in the 20–130 eV photon energy range. From a comparison of experimental and theoretical conduction band densities of states it is found that in the measured composition range the trends of the rigid band model behavior are respected.     

From the infrared to the visible range: Spectroscopic studies of ytterbium doped oxyborates

The spectroscopic study of yttrium oxyborates doped with trivalent ytterbium is conducted in the UV-Visible and infrared range. The multiplicity of the ytterbium environments in the studied compounds leads to complex emission spectra in the infrared and excitation spectra in the ultraviolet. Different ²F_5/2 and ²F_7/2 transitions have been pointed out. The emission extends up to 1090 nm for one compound. A correlation was evidenced between position and de-excitation mode of a charge transfer band and ytterbium environment for both oxyborates. Decay time dependence as a function of ytterbium concentration is also reported. For the highest concentration, a blue-green luminescence can be observed under strong IR excitation. Its study revealed two possible mechanisms: erbium ion emission at 550 nm after up-conversion and cooperative luminescence of ytterbium ions.     

Vibrational moments of fundamental transitions in low-temperature molecular liquids: Determination from the band shape of vibrations in the overtone spectral range

It is shown that the integrated absorption coefficients of strong fundamental bands of some gaseous substances can be determined with an accuracy of 5–10% using experimental data on the spectral moments of bands in the overtone spectral range of these substances in the liquid phase near the melting point. The absorption coefficients are calculated within the framework of the cell model of the liquid state from the contributions of the resonance dipole-dipole interaction to the second spectral moment. The combination and overtone absorption bands of the SF₆, CF₄, SiF₄, NF₃, CHF₃, CC1F₃, CBrF₃, OCS, N₂O, and CO₂ molecules in the liquid state and in solutions in liquefied Xe, Kr, and O₂ are recorded. The data in the literature on the intensity of strong IR bands in the gas phase are analyzed. Using an improved experimental technique, additional measurements are performed. It is found that the absorption coefficients determined from the spectral characteristics of the liquids agree well with the coefficients measured in the gas phase.     

Application of the nuclear field theory to monopole interactions which include all the vertices of a general force

The field treatment is applied to the monopole pairing and monopole particle-hole interactions in a two-level model. All the vertices of realistic interactions appear, and the problems treated here have most of the complexities of real nuclei. Yet, the model remains sufficiently simple, so that a close comparison with the results of a (conventional) treatment in which only the fermion degrees of freedom are considered is possible. The applicability to actual physical situations appears to be feasible, both for schematic or realistic forces. The advantage of including the exchange components of the interaction in the construction of the phonon is discussed.