The Lamb-dip spectrum of methylcyanide: Precise rotational transition frequencies and improved ground-state rotational parameters

Methylcyanide, CH₃CN, is an important interstellar species, and therefore the accurate knowledge of precise rest frequencies for rotational transitions as well as ground-state rotational and hyperfine constants is needed. In this work the hyperfine structure of the millimeter- and submillimeter-wave spectra of CH₃CN has been further investigated. In addition, accurate THz measurements have been carried out for the first time. Consequently, the present investigation allowed us to provide the most accurate ground state rotational and hyperfine parameters known at the moment for CH₃C¹⁴N. To resolve the hyperfine structure of the rotational transitions observed, the Lamb-dip technique has been exploited. Both frequency-modulated and video-type detections have been employed.     

Modeling of hydrogen ground state rotational and vibrational temperatures in kinetic plasmas

A dipole-quadrupole electron-impact excitation model, consistent with molecular symmetry rules, is presented to fit ro-vibronic spectra of the hydrogen Fulcher-α Q-branch line emissions for passively measuring the rotational temperature of hydrogen neutral molecules in kinetic plasmas with the coronal equilibrium approximation. A quasi-rotational temperature and quadrupole contribution factor are adjustable parameters in the model. Quadrupole excitation is possible due to a violation of the 1st Born approximation for low to medium energy electrons (up to several hundred eV). The Born-Oppenheimer and Franck-Condon approximations are implicitly shown to hold. A quadrupole contribution of 10% is shown to fit experimental data at several temperatures from different experiments with electron energies from several to 100 eV. A convenient chart is produced to graphically determine the vibrational temperature of the hydrogen molecules from diagonal band intensities, if the ground state distribution is Boltzmann. Hydrogen vibrational modes are long-lived, surviving up to thousands of wall collisions, consistent with multiple other molecular dynamics computational results. The importance of inter-molecular collisions during a plasma pulse is also discussed.     

Hyperfine structure of the J=1←0 transition of HCl and HCl: improved ground state parameters

The pure rotational J=1←0 transitions of H³⁵Cl and H³⁷Cl have been observed in the millimeter-wave region using the Lamb-dip technique to resolve the hyperfine structure due to ³⁵Cl or ³⁷Cl and H. The present observations allow to provide not only very accurate hyperfine constants but also, joint together with previous data, the most accurate ground state rotational parameters known up to now. The experimental determination of the hyperfine parameters has also been supported by ab initio computations.     

The pure rotational spectrum of Difluoroiodomethane, CHF2I

The pure rotational spectrum of CHF₂I has been recorded for the first time, in a supersonic expansion in the region 1.7-17 GHz, and at room-temperature in the region 302-318 GHz. The observed transitions span the values of J^″ from 0 up to 67. Precise rotational and centrifugal distortion constants have been determined. Furthermore, the complete iodine nuclear electric quadrupole coupling tensor, in the inertial and principal axes, has been determined. Quantum chemical calculations have been performed to aid with the analysis. Iodine quadrupole mediated perturbations have resulted in the following observations: (i) several transitions having enhanced intensities and (ii) the observation of several forbidden, ΔJ=±2, transitions. Comparisons in electronic structure are made between the series of molecules CH_3-nF_nX; and X = Cl, Br, I.     

The isotopic dependence of the spin-rotation interaction: the rotational spectrum of cadmium hydride in its XΣ state

Far-infrared rotational transitions within the X²Σ⁺ (v=0) state of cadmium hydride (CdH) were recorded over the range N″=2-17 for 12 different isotopomers, using the technique of tunable far-infrared (TuFIR) spectroscopy. The molecule was made by heating cadmium metal in the presence of a DC electric discharge in hydrogen. Fine structure arising from the electron spin-rotation interaction and hyperfine structure from the ¹¹¹Cd, ¹¹³Cd, and ¹H nuclei were resolved and analyzed. All of the isotopic data were fitted together using a Hamiltonian containing mass-independent, Dunham-type rotational parameters U_kl and small correction terms Δ_kl described by Watson [J. Mol. Spectrosc. 80 (1980) 411]. The spin-rotation interaction was modeled in an analogous way using Dunham-like U_γ,kl parameters, and fitting its isotopic dependence properly required the use of four Δ_γ,kl correction terms.     

Ground state parameters of BiH3 from infrared and millimeter-wave spectra: ground state and equilibrium structures

Unstable, short-lived BiH₃ has been synthesized and investigated by rotational spectroscopy in the range 158 (J=1-0) to 1280 GHz (J=8-7). Quadrupole and spin-rotation hyperfine structures (eQq=584.676(96) MHz), and the A₁A₂ splitting of the K=3 ground state level, have been resolved. By merging the pure rotational data with 1764 ground state combination differences obtained from the analysis of high resolution Fourier transform infrared spectra of the ν₁-ν₄ bands [J. Mol. Spectrosc. (2004) (in press)] spanning J and K values up to 16 and 14, respectively, with 0?ΔK?9, the ground state rotational and centrifugal distortion constants up to octic and sextic terms for reductions A and B, respectively, have been determined. Of the reductions of the ground state rovibrational Hamiltonian, reduction B including ε rather than h₃ as off-diagonal element is clearly favored. An experimental r₀ structure of the very-near spherical oblate symmetric top BiH₃, r(BiH)=178.82 pm and α(HBiH)=90.320°, has been deduced from the rotational constants B₀=2.64160172(18) and C₀=2.6010403(31) cm⁻¹. The derived experimental r_e structure, r_e(BiH)=177.834(50) pm and α_e(HBiH)=90.321(10)°, was determined. This is in excellent agreement with the most recent ab initio structure, r_e(BiH)=177.84 pm, and α_e(HBiH)=90.12°.     

Assignment and analysis of the rotational spectrum of 3-chlorobenzonitrile

The rotational spectrum of 3-chlorobenzonitrile has been assigned and measured over the frequency region 9-290 GHz, both in the static sample and in supersonic expansion. Extensive measurements are reported for the ground states of the ³⁵Cl and the ³⁷Cl isotopomers. Precise spectroscopic constants have been determined from global fits to all available data, including resolved hyperfine splitting structure due to the presence of the chlorine and the nitrogen quadrupolar nuclei. Principal nuclear quadrupole tensors are derived for both ³⁵Cl and ¹⁴N nuclei in the parent isotopomer, and the results are compared with those for related molecules. The values of all spectroscopic constants are confronted with predictions from ab initio calculations in order to assess the utility of the array of simple techniques employed to increase quantitative accuracy of such predictions.     

The millimetre-wave rotational spectrum of phenylacetylene

The room-temperature rotational spectrum of phenylacetylene (C₆H₅CCH), was studied at frequencies up to 340 GHz. Extensive new measurements, covering rotational transitions with quantum number values up to J=140 and K_a=59, allowed determination of precise spectroscopic constants for the ground state and for the lowest two excited vibrational states, v₂₄=1 and v₃₆=1. The two excited states belong to the lowest B₁ and B₂ symmetry normal modes and their rotational transitions are very strongly perturbed by a-axis Coriolis resonance. A successful fit of the resonance is reported, resulting in and , in good agreement with results of ab initio computations.     

The ground state rotational constants of NNO

We report new measurements of the 5 ← 4 through 9 ← 8 lines in the pure rotational spectrum of nitrous oxide, ¹⁵N¹⁵N¹⁶O, and measurements at room temperature and at an elevated temperature of the 10⁰0-00⁰0 and 02⁰-00⁰0 bands of that molecule. The new data together with data for 10 other vibration-rotational transitions which previously have been reported enable us to determine the ground state constants. Using the newly determined values of B₀₀₀, D₀₀₀, and H₀₀₀, we have determined the band origins and the upper state constant differences B - B₀₀₀, D - D₀₀₀, and H - H₀₀₀ of 25 vibration-rotational bands whose lower level is the ground vibrational state.     

Estimation of rotational temperature of the source emitting the spectrum of PbO molecule

The (1, 0), (0, 1) and (0, 2) bands ofD→X system of lead monoxide have been excited in RF discharge source and photographed in the seventh order of a 2-meter PGS. Intensity records of the rotational lines have been obtained. Rotational constants and the intensity measurements ofQ andP branch lines of the above three bands andJ numbering are used to calculate the effective rotational temperature of the source emitting the spectrum of²⁰⁸Pb¹⁶O molecule.     

Extended analysis of hydroxyacetone in the torsional ground state

The torsion-rotation spectrum of hydroxyacetone presents a highly challenging analysis problem in molecular physics. Continuing analyses of this species are compelling due to a nascent interest from astronomers, who believe hydroxyacetone may link a variety of organic chemical families observed in the interstellar medium (ISM). Recent work has demonstrated the difficulties in analysis of the millimeter spectrum, and the modestly weaker spectrum in this region has not afforded an ISM detection. We present an extension of the laboratory measurements and analysis up to the room temperature Boltzmann peak near 300 GHz, thus providing sufficient coverage to examine the ISM for the strongest features expected in star-forming hot cores. Even without subsequent detection, searches for the stronger features will produce the lowest possible upper limits of this elusive species.     

Covalent binding parameters and the ground state wavefunctions of vanadyl ion complexes

The Steven’s method of molecular orbitals for octahedral complexes containing transition metal ions has been used for estimating the binding parameters and interpreting theg factors of VO ₂ ⁺ ion in single crystals. The expressions forg factors have been given in terms ofK _‖ andK _⊥ taking into account the tetragonal crystalline field and covalent binding effects. Computations show thatK _⊥ should be less than 0.066 in order to fit the experimentalg values. The ground state wave function (GSWF) of VO ₂ ⁺ ion doped in different single crystals has been estimated using crystal field theory. The GSWF is found to be ind _xy state with slight admixture of the excited states ,d _xz andd _yz. The hyperfine interaction parameterP and Fermi contact termX have also been estimated.     

Comparison of the relative accuracy of the potential energy curve of hydrogen fluoride from ab initio calculations and from an empirical “universal” function

The accuracy of recent theoretical calculations of the potential energy curve of hydrogen fluoride is compared to that of the potential predicted by a previously proposed empirical Morse-like function, universally applicable to stable ground state diatomics. In addition to the properties required for the Morse equation (bond energy, bond length, vibrational frequency, and mass) two more properties are used by the empirical function: the electronegativity difference and the product of Slater’s effective nuclear charges of the two atoms. Eigenvalues obtained from the most successful of recent ab initio calculations and from the empirical function are compared to experimental vibrational term values, as a stringent test of accuracy. The accuracy of the empirical “universal” function is marginally superior.     

The pure rotational spectrum of ZnS (XΣ)

The pure rotational spectrum of ZnS (X¹Σ⁺) has been measured using direct-absorption millimeter/sub-millimeter techniques in the frequency range 372–471 GHz. This study is the first spectroscopic investigation of this molecule. Spectra originating in four zinc isotopologues (⁶⁴ZnS, ⁶⁶ZnS, ⁶⁸ZnS, and ⁶⁷ZnS) were recorded in natural abundance in the ground vibrational state, and data from the v = 1 state were also measured for the two most abundant zinc species. Spectroscopic constants have been subsequently determined, and equilibrium parameters have been estimated. The equilibrium bond length was calculated to be r_e  2.0464 Å, which agrees well with theoretical predictions. In contrast, the dissociation energy of D_E  3.12 eV calculated for ZnS, assuming a Morse potential, was significantly higher than past experimental and theoretical estimates, suggesting diabatic interaction with other potentials that lower the effective dissociation energy. Although ZnS is isovalent with ZnO, there appear to be subtle differences in bonding between the two species, as suggested by their respective force constants and bond length trends in the 3d series.     

高恢复压力氟化氘增益发生器技术研究

增益发生器是影响高能氟化氘(DF)化学激光器恢复压力的核心组件,采用传统增益发生器的DF激光器尾气恢复压力约为6.7 kPa。设计了一种紧凑化TRIP型增益发生器,突破了高腔压运转、主气流气幕和激射腔边壁回流抑制等关键技术,实现了DF激光器尾气恢复压力的大幅提高。实验结果表明,在面积比流量为1.3~3.3 g·s^-1·cm^-2的范围内,随着增益发生器面积比流量的提高,激光器尾气恢复压力有效提高,面积比功率持续增加;在面积比流量为3.3 g·s^-1·cm^-2条件下,DF激光器可以实现26.7 kPa背压(海拔10 km大气压)下的高效运行。     

The rotational spectrum of tertiary-butyl alcohol

The rotational spectrum of tertiary-butyl alcohol has been recorded in selected regions between 8 and 500 GHz. Early data from the University of Wisconsin in the 8-40 GHz region have been combined with recent measurements from the University of Bologna and the Jet Propulsion Laboratory in the millimeter and submillimeter wavelength regions. The spectrum was fit over a wide range of J’s and K’s using a common set of parameters for both the A and E states. This paper describes the initial assignment at Wisconsin and the final procedure used to assign and fit the higher rotational states. The resulting molecular constants and their interpretation are discussed.     

g-factors of the ground state rotational band of158Dy

Theg-factors of the four lowest states of the ground state rotational band of¹⁵⁸Dy have been determined asg(2 ₁ ⁺ )=+0.362(23),g(4 ₁ ^su+ )=+0.340(20),g(6 ₁ ^su+ )=+0.207(36) andg(8 ₁ ^su+ )=+0.21(11). Theg-factors of the 2⁺ and 4⁺ states were measured by the IPAC method with radioactive samples of 2.4 h¹⁵⁸Er in external magnetic fields. To investigate the higher states, for the first time an on-line γ—γ IPAC experiment was performed with the reaction¹⁵⁶Gd(α, 2n)¹⁵⁸Dy by use of the static hyperfine field of DyGd.     

The rotational levels of the ground vibrational state of formaldehyde

A variational procedure for rovibrational energy levels and wavefunctions of centrally connected tetra-atomic molecules is extended to include high rotational states, and in particular, J ? 10 levels for the vibrational ground state of formaldehyde. It is very important to do this because it has made possible the calculation of the usual rotational spectroscopic constants which correspond to the forcefield and geometry. A direct comparison with the ‘observed’ spectroscopic constants is therefore possible. The geometry and forcefield are refined against 65 J = 0 levels of H₂CO, 6 J = 0 levels of D₂CO, 42 J = 1, 70 J = 2 and 98 J = 3 levels of the ground and fundamentals of H₂CO and D₂CO, using an iterative scheme. The mean absolute error of the J = 0 levels is 1·10 cm^?1 and that for J ≠ 0 is 0·005 cm^?1, and the predicted geometry is CH = 1·10064 Å, CO = 1·20296 Å and HCO = 121·648°. Finally, the rotational constants A, B, and C for the ground state are 281956, 38846 and 34003 MHz, compared with the observed values 281971, 38836, and 34002 MHz. The centrifugal distortion constants Δ_J , Δ_JK , Δ_K and δ_J , are 77, 1275, 18113 and 11 kHz compared with 75, 1291, 19422 and 10 kHz. These results underline the accuracy of the new quartic forcefield.