The microwave spectrum of methyl isothiocyanate

The microwave spectrum of methyl isothiocyanate, CH₃NCS, has been measured in the range from 5 to 26 GHz. Almost 300 lines have been assigned to the a-type J + 1 ← J rotational transitions (J = 0 to 4) arising from molecules in the ground state and excited torsional and CNC bending states. The observed spectrum has been analyzed and successfully interpreted in terms of the five-dimensional quasi-symmetric top molecule model accounting explicitly for the large-amplitude CNC bending motion, and internal and overall rotation. In the least-squares fitting to the observed transition energies the values of the parameters of the CNC bending-torsional potential function have been determined.     

Methyl isocyanate: An analysis of the low-J rotational spectrum using the quasi-symmetric top molecule approach

The low-J rotational spectrum of methyl isocyanate (CH₃NCO) has been analyzed in terms of the quasi-symmetric top molecule model, accounting explicitly for the large-amplitude CNC bending motion, and internal and overall rotation. An assignment of 25 J = 1 ← 0 and 2 ← 1 rotational transitions arising from the various CNC bending and torsional states is proposed. The molecule is found to be a nearly freely internally rotating quasi-symmetric top, with a barrier to linearity of the CNCO skeleton of 1049 cm^?1 and an equilibrium CNC valence angle of 140.2°.     

The Emission Spectrum of Hot Water in the Region between 370 and 930 cm−1

An emission spectrum of the water molecule at a temperature of 1550°C has been recorded in the range from 373 to 933 cm⁻¹. More than 4000 pure rotational lines were observed with the strongest belonging to the ground state (000) and the first excited bending vibrational level (010). Transitions involving rotational quantum numbersJandK_asignificantly higher than previously recorded have been assigned.     

Microwave spectrum of CH3OD

The microwave spectrum of CH₃OD has been observed in the frequency region between 14 and 92 GHz. All the ground-state transitions with J ≤ 8 and J = 2 ← 1, a-type transitions in the excited torsional states (v = 1 and v = 2) have been observed. The spectrum has been analyzed and rotational constants, torsional constants, torsion-vibration-rotation interaction constants, and centrifugal distortion constants have been evaluated. The Stark effect measurements have been made and the dipole moment components have been determined as μ_a = 0.833 ± 0.008 D and μ_b = 1.488 ± 0.015 D.     

The microwave spectrum of trifluoroacetonitrile in excited vibrational states

The microwave transitions J → J + 1 have been observed in the symmetric top molecule trifluoroacetonitrile, CF₃CN, for molecules excited into several of the low-lying vibrational states. Measurements made in the degenerate states v₇ = 1 v₈ = 1 have been fitted to the formula derived by Grenier-Besson and Amat (1) for transitions J → J + 1 in degenerate vibrational states of molecules with C_3v symmetry. The measurements for the state v₈ = 1 have been extended to 150 GHz where it is shown that the above formula becomes inadequate to describe accurately the observed spectrum.     

High-resolution inverse Raman spectroscopy of the ν1 band of water vapor

The Raman spectrum of the ν₁ band of water vapor at 7 Torr and 296 K, and at 84 Torr and 404 K, has been measured using high-resolution inverse Raman spectroscopy. The frequencies and relative intensities of the observed transitions are compared to a spectral model based on infrared data. Self-broadening coefficients have been determined for 22 lines from J = 0 to J = 8.     

An investigation of centrifugal distortion in the microwave spectrum of formamide

Measurements of the microwave spectrum of formamide have been extended in order to account accurately for the effects of centrifugal distortion. A total of 22 new transitions involving J ≤ 29 have been measured for ¹⁴NH₂¹²CH¹⁶O in the ground vibrational state. Combined with previous observations, these transitions have been fit to a model containing five quartic distortion terms and seven sextic terms with a rms deviation of 64 kHz. A large number of resolved quadrupole shifts were fit with an rms deviation of 42 kHz. The remainder of the spectrum for J ≤ 30 has been calculated with standard deviations less then 3 MHz. Correct weighting of the observed transitions has been found to be important.     

The microwave spectrum of germyl isocyanate,a quasi-symmetric top

The microwave spectrum of germyl isocyanate in the K, P, and R bands (12.4–40.0 GHz) has been investigated using natural isotopic samples and samples containing specific germanium isotopes, mass numbers 72 and 74, and samples containing GeD₃ groups. The very complex spectrum is analyzed as that of a quasi-symmetric top, in which the skeletal bending motion has an energy maximum at the linear configuration; the height of the maximum is some 339 cm⁻¹. Many vibrational states of the two-dimensional bend lie close in energy, resulting in strong interactions between rotational levels of different vibrational states. The program used for the analysis has been used previously to account for similar spectra of methyl and silyl isocyanates and methyl isothiocyanate; the behavior of the germyl compound is more like that of the methyl isocyanate than that of the silyl compound, where the height of the maximum is much less. Although we did not include centrifugal distortion operators in the Hamiltonian the program successfully predicts k = 0 line positions in J + 1 ← J bunches with J up to 9, using only lines in the J = 3 bunch to define the parameters of the model, which include the height of the hump, the bend angle of the skeleton at the energy minimum (142.18(5)°), the force constant for the bending motion at the minimum (0.1094(7) mdyn Å), and the GeN bondlength at equilibrium (1.8257(5) Å). The threefold barrier to internal rotation of the GeH₃ group at the equilibrium position is about 3 cm⁻¹, much lower than the value found for methyl isocyanate. The fit to the observations, about 100 lines in the 4 ← 3 bunch, is improved by allowing for a variation in the GeN bondlength as the bend angle changes. The quality of the least-squares fit corresponds to an estimated standard deviation for an observation of about 2 MHz, but not all observed lines can be accounted for precisely, showing that additional interactions are involved that are not yet included in the model.     

The microwave spectrum of trioxaadamantane

The microwave spectrum of 2,8,9-trioxaadamantane has been investigated in the region from 12.4 to 26.5 GHz. The observed spectrum exhibited the expected symmetric top pattern, with the rotational constant B₀ = 1848.64 MHz. Numerous weaker lines were observed and were attributed to vibrational satellites of the main rotational transition. The transitions from J = 3 → 4 through J = 6 → 7 were studied and no centrifugal distortion effects were observed.A structure is derived that is consistent with the observed rotational constants of the normal and one isotopic species by use of the method of diagnostic-least-squares.The second order stark effect for the K = 0 state yielded a dipole moment of 3.01 ± 0.03 D.     

Inelastic neutron scattering study of acoustical magnons in MnFe2O4

The room-temperature spin wave spectrum in MnFe₂O₄ has been investigated by means of inelastic neutron scattering using the time-of-flight technique. The acoustical branch could be obtained in the [100]- and the [110]-directions up to nearly the Brillouin zone boundary. Values for the effective exchange parameters J_AB and J_BB have been derived. In both symmetry directions some low lying phonon branches could also be observed.     

Fourier Transform Infrared spectrum of the OCD bending mode in methanol-D1

The infrared (IR) spectra corresponding to OCD bending vibration of asymmetrically deuterated methanol species CH₂DOH have been recorded with a Fourier Transform Spectrometer. The spectrum shows a typical structure of a parallel a-type band. This is expected because the bending vibration mainly executed parallel to the symmetry axis The Q-branch lines are grouped closely around 896 cm⁻¹ and the P- and R-Branches show complex structure. Nonetheless it was possible to assign a-type P- and R-branch lines up to K value of 8 and J value up to about 20 in most cases. The Q-branch lines for higher K values can be followed to about J = 15, the presence of which confirmed the assignments. The observations suggest that in the OCD bend some energy levels are highly interacted by highly excited torsional state from the ground torsional state. A full catalogue is presented along with the effective molecular parameters. An intensity anomaly was also observed in the transitions. So far it has been possible to assign only transitions between e₀ ← e₀ states. Plausible explanations of intensity anomaly are presented. Lastly, a number of optically pumped far infrared (FIR) laser lines have been assigned either to exact or tentative quantum states. These assignments should prove valuable for production of new FIR laser lines.     

Can the incident photo-to-electron conversion efficiency be used to calculate short-circuit current density of dye-sensitized solar cells

The relationship between the integration of the incident photo-to-electron conversion efficiency (IPCE) and the measured short-circuit current density (J_SC) of dye-sensitized solar cell (DSC) has been analyzed. The J_SC of DSC under full sun is usually considered to be determined by the overlap between its spectral IPCE and the spectral photon flux incident on the cell. However, the IPCE spectrum has been found to be influenced by the bias light intensity in many practical cases. Through theoretical deduction, we have proved that J_SC calculated from IPCE spectrum is related to the slope at corresponding incident light intensity on the short-circuit photocurrent density–incident light intensity (J_SC?E_light) curve. The equal relation between J_SC calculated from IPCE and J_SC practically measured can only be obtained when the J_SC?E_light curve is a straight line through the origin of the coordinates. The measured results of four DSC samples with different working condition show a good agreement with the theory. In addition, a simple method to validate the accuracy of IPCE measurement is also demonstrated.     

The ν6 parallel band of cyclopropane at 3100 cm−1

The ν₆ fundamental of cyclopropane has been recorded on a 4.5-m vacuum spectrometer. Deconvolution of the spectrum has revealed considerably more detail than found in previous investigations. New information of a qualitative nature has been learned about the highly perturbed upper state and improved values of the band center and the upper-state rotational constant have been obtained. A lower-state combination-difference analysis using J values up to J = 23 has resulted in values of B″ and D″_J which are in excellent agreement with recent investigations. The following values of molecular constants, in wavenumber units (cm^?1), have been determined: B″ = 0.67023, D″_J = 0.93 × 10^?6, ν₀ = 3101.529, and B′ ? B″ = ?0.0019. The present data have been used with data from recent Raman and infrared spectra of C₃H₆ in a combined least-squares fit to the ground-state constants.     

The Fourier spectrum of CH3OH: The region between 8 and 40 cm−1

The experimental Fourier spectrum of CH₃OH has been investigated between 8 and 40 cm^?1. Good agreement was found between the experimental measurements and the results of the computational routines available up to now when low J values (J ? 10) are involved. At higher J, the line assignments are possible by means of Taylor expansions of the energy levels. A catalog of almost 1500 lines, two-thirds of which have been assigned, is presented.     

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.     

Pure rotational spectrum of cyanopropyne in the v12 = 1 vibrational state

The micoowave and millimeter-wave spectrum of cyanopropyne, CH₃CCCN, in the lowest excited vibrational state, v₁₂ = 1 (E), has been observed in the frequency range from 8 to 220 GHz. The measurements up to the J = 53−52 transitions allowed us to determine the Coriolis coupling term and the l-type interaction term very precisely in addition to some of the sextic centrifugal terms. The contribution of the r-type interaction (Δk = ±1, Δl = ±2) has been found to be correlated with that of η_J, a centrifugal correction term to the first-order Coriolis interaction.     

The forbidden (J → J + 1) spectrum of CH4 in the ground vibronic state

The pure rotational R-branch spectrum of CH₄ arising from the centrifugal distortion moment has been studied using a simple 12.10-m light-pipe cell and a conventional interferometer. Ten forbidden (J → J + 1) transitions for J = 7 to J = 16 have been observed in the spectral region 80–200 cm^?1 with a theoretical resolution of 0.5 cm^?1. The integrated intensity of the six strongest lines has been measured and was found to be of the order of twice that calculated from the distortion moment obtained earlier from a molecular beam study of the (J = 2) rotational level. In the approximation that frequency shifts due to this excess intensity are neglible, it has been determined that the rotational constant B₀ = (5.245 ± 0.004) cm^?1 and the scalar distortion constant D_S = (1.19 ± 0.09) × 10^?4 cm^?1. It is argued that the excess intensity is due to higher-order terms in the dipole moment operator and the validity of the frequency analysis is considered in this context.     

Stark spectroscopy of 13CD3OH with the HCN laser

The laser Stark spectrum of ¹³CD₃OH has been studied using the 311 μm line of the HCN laser. An extensive series of absorption lines has been observed and assigned to the J = 3 to 11 members of the K = 2 ← 3E₁, Q-branch transition in the v_t = 1 excited torsional state. Zero-field frequencies for all the assigned transitions are given with improved accuracy over those calculated from available molecular constants. For the Q-branch series, the branch origin and the series expansion coefficients are also presented.     

Dispersion of acoustical magnons and phonons in Mn1.7Fe1.3O4

The room-temperature spin wave spectrum has been investigated in Mn_1.7Fe_1.3O₄ by means of inelastic neutron scattering. The acoustical branch could be obtained in the symmetry directions. Values for the effective exchange parameters J_AR and J_RR have been derived. Some acoustical phonon branches could also be observed and the elastic constants C₄₄ and (C₁₁ – C₁₂) were estimated.     

The two-dimensional anharmonic oscillator: The microwave spectrum of silyl isocyanate,SiH3NCO

The J + 1 ← J transitions (J = 2, 3, 4, 5, and 6) in the microwave spectrum of SiH₃NCO have been assigned for the vibrational ground state and for the vibrational states v₁₀ = 1, 2, and 3. The results for v₁₀ = 0 confirm earlier work. The vibration-rotation constants show a remarkable variation with v₁₀ and l₁₀. To a large extent the anomalous behavior of these constants has been explained in terms of a strongly anharmonic potential function for the ν₁₀ vibrational mode.