The Rotational Spectrum of H2Te

In the present work, we study the spectrum of the H₂Te molecule in the submillimeter-wave and far infrared region. An important aim of this investigation is the further experimental characterization of the anomalous “four-fold cluster effect” exhibited by the rotational energy levels in the vibrational ground state of H₂Te. The spectrum in the region 90–472 GHz was measured with a source-modulated millimeter-wave spectrometer and that between 600 and 1600 GHz with a far-infrared sideband spectrometer. The far infrared spectrum from 30 to 360 cm⁻¹was measured with a Bruker IFS 120 HR interferometer attached to a 3 m long cell. We have assigned 224 submillimeter-wave lines and 1695 FIR lines. These observed data were supplemented by a large number of ground state combination differences derived from rotation–vibration bands of H₂Te, and the resulting large data set was analyzed by means of a modified Watson Hamiltonian. Accurate sets of rotational and centrifugal distortion constants for all eight tellurium isotopomers were obtained.     

Resonance-enhanced multiphoton ionization (REMPI) spectroscopy of the Cl and Cl isotopomers of p-chloroanisole

The geometric structures and vibrations of p-chloroanisole isotopomers in the first electronically excited state were studied by mass-analyzed resonance-enhanced two-photon ionization spectroscopy and by theoretical calculations. The band origins of the S₁ ← S₀ electronic transitions of ³⁵Cl and ³⁷Cl isotopomers were found to be equivalent at 34 859 ± 3 cm⁻¹. Assignments of the observed vibrational bands of the two isotopomers were made mainly based on the CIS/cc-PVDZ calculations and on conformity with the available data in the literature. Although the general spectral features of these two isotopomers are similar, the frequencies of some vibrational modes are different. This frequency shift partially depends on the degree of involvement of the chlorine atom in the molecular vibrations.     

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.     

Microwave spectrum and structure of methyl phosphonic difluoride

The rotational spectrum of methyl phosphonic difluoride has been reinvestigated using a pulsed-molecular-beam Fabry-Perot cavity microwave spectrometer. The enhanced resolution of the Fourier transform microwave (FTMW) spectrometer (compared to the original work done in a conventional Stark spectrometer) has allowed the measurement of small A-E splittings of many of the rotational transitions caused by the internal rotation of the methyl top. The barrier to internal rotation, V₃ = 676 (25) cm⁻¹, has been determined experimentally from the A-E splittings of the rotational transitions in the ground vibrational state. This barrier height is substantially lower than the previously determined value for the barrier, which was 1252 (14) cm⁻¹. High-level ab initio calculations at the MP2/aug-cc-pVTZ level predict a barrier to internal rotation of 638 cm⁻¹, in agreement with the experimentally determined value found here. The high sensitivity of the FTMW spectrometer has also permitted the measurement of the ¹³C and ¹⁸O isotopomers in natural abundance. The addition of these two isotopomers has allowed an improved structural determination.     

Infrared Transitions of HCN and HCN between 500 and 10 000 cm

We have measured the Fourier transform spectrum (FTS) of two isotopomers of hydrogen cyanide (H¹²C¹⁴N and H¹²C¹⁵N) from 500 to 10 000 cm⁻¹. The infrared data have been combined with earlier published microwave and submillimeter-wave measurements. From this analysis new vibration–rotation energy levels and constants are given, based on the observation of a number of new vibrational levels, especially for H¹²C¹⁵N. The Coriolis interaction involving Δv₃= −1, Δv₂= 3, and Δl= ±1 has been observed for a great many levels and in some cases the assignments of laser transitions allowed by this interaction are more clearly shown. New vibration–rotation constants are given that allow one to predict the transition wavenumbers for most of the transitions below 10 000 cm⁻¹with accuracies of about 0.5 cm⁻¹or better. Values are given for the power series expansion of thel-type resonance constants and for the centrifugal distortion constants, as well as the usual vibrational and rotational constants.     

Analysis of ν2 of H2Se

The infrared absorption spectrum of ν₂ of H₂Se in the region from 885 to 1347 cm^?1 was obtained with a resolution limit of 0.025 cm^?1 on the University of Denver 50-cm FTIR spectrometer system. We have assigned 1604 lines for the six isotopomers of H₂Se, including 25 lines for the H₂⁷⁴Se isotopomer, and have analyzed them using Watson's A-reduced Hamiltonian in the I^r rotational representation. Ground state constants for each of the five most abundant isotopomers were obtained from fits of microwave transitions combined with weighted averaged ground state combination differences formed from the infrared bands (010), (020), (100), and (001). Upper state constants for each of the five most abundant isotopomers were obtained from least-squares fits of the spectral lines of ν₂, keeping the ground state constants fixed to the values determined from our ground state fits. An alternate set of ground state constants together with isotopic mass adjustment constants for all six isotopomers was determined by simultaneously fitting all available microwave transitions and infrared ground state combination differences. Keeping this set of ground state constants fixed, a single set of upper state constants and isotopic mass adjustment constants for the ν₂ band was determined by a simultaneous fit of infrared spectral lines from all six isotopomers.     

Microwave spectrum and barrier to internal rotation of 1-chloro-2-butyne

Rotational transitions of the μ_a and μ_b type have been identified with microwave-microwave double resonance measurements for 1-chloro-2-butyne in the ground vibrational state. In the first excited state of the methyl torsion only μ_a-type transitions have been identified. The A-type transitions of the ground vibrational state can be described perfectly by the rigid rotor approximation with centrifugal corrections. Using the internal axis method the barrier to internal rotation was determined from the A,E splittings: V₃ = 10.05 ± 0.09 cm⁻¹. A model which allowed for geometry relaxation upon internal rotation was used to fit one set of parameters to the transition frequencies of both ground state and first excited torsional state. The sixfold contribution to the barrier was found to be negligible: V₆ = −0.4 ± 0.3 cm⁻¹.     

FTS-Raman flame spectroscopy of high-J lines in H2 and D2

High-J rotational transitions in the ground vibrational state of molecular hydrogen and deuterium have been recorded using the FTS-Raman technique. Transitions above those recorded previously at room temperature were observed in diffusion flames burning H₂ with air, and D₂ with air. For H₂ the v = 0-0 S(6) and S(7) transitions, which had not been observed previously, were recorded in the flame spectra. For D₂ the flame spectra yielded measurements of the S(7) through S(12) lines for the first time. By combining flame and room-temperature Raman and infrared measurements it has been possible to improve H₂ ground state rotation constants to fifth order. For D₂, the combination of flame and room-temperature Raman measurements required an extension to fifth-order constants, as compared with the third-order fit which was adequate for the room-temperature data alone. Our improved line positions can be applied to transitions observed in the Orion Molecular Cloud.     

Accurate relations for the isotopically invariant spectroscopic parameters of diatomic molecules

Equations are obtained relating the isotopically invariant spectroscopic parameters U_mj, which must be considered as conditions in the least-squares method in spectral analysis. Expressions are given for the first seven Dankhem potential parameters in terms of U_m0 and U_m1. The contribution to the spectroscopic coefficients Y_mj due to violation of the Born-Oppenheimer approximation is calculated for¹²C¹⁶O.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 18–21, November, 1984.It remains to thank Yu. S. Makushkin, V. Ya. Galin, andV. F. Golovko for valuable discussions of the work.     

The far-infrared spectrum and spectroscopic parameters of PH3 in the ground state

The far-infrared spectrum of phosphine, PH₃, was recorded in the region between 30 and 200 cm⁻¹ at a resolution of 0.002 cm⁻¹. ΔJ = +1, ΔK = 0 rotational transitions in the ground state were measured and assigned up to J″ = 22 and K = 19. These transitions were analyzed together with the presently available microwave and submillimeter-wave data on the basis of different formulations of the rotational Hamiltonian, which included Δk = ±3 and/or Δk = ±6 interaction terms. An upper limit for the constant of the inversion splitting was obtained by fitting the same transitions to an appropriate inversion-rotational Hamiltonian. Rotational transitions in the v₂ = 1 and v₄ = 1 vibrational states were also observed.     

New ground state constants of CH3Cl and CH3Cl from global polyad analysis

A global analysis of the infrared spectrum of chloromethane involving the ground state and the 13 vibrational states lying up to 2600 cm⁻¹ was recently achieved using high resolution Fourier transform spectra of pure isotopomers. More than 20 000 transitions (cold and hot bands) for each isotopomer ¹²CH₃³⁵Cl and ¹²CH₃³⁷Cl have been assigned and fitted with a standard deviation of about 3 × 10⁻⁴ cm⁻¹ close to the experimental precison. As part of this global effort, improved ground state constants up to sextic centrifugal distortion terms have been determined for each isotopomer taking advantage of the numerous allowed and perturtation-allowed transitions simultaneously fitted using our global model. The axial constants could be determined from ΔK ≠ 0 combinations arising from rovibrational local resonances within Polyads 3 and 5.     

Isotopically invariant dunham parameters and the potential function of the HCl molecule

The isotopically invariant Dunham parameters U _mj , Δ _mj ^H and Δ _mj ^Cl were determined by simultaneously fitting the line centers of vibration-rotation transitions of six isotopic HCl forms in the ground electronic state. Fitting included relations between U _mj values. The parameters of the isotopically invariant potential of HCl were determined using independent U _m0 and U _m1 values. The contributions to the vibrational terms of H³⁵Cl caused by violation of the Born-Oppenheimer approximation were calculated.     

The Sn, Sn and Sn nuclear spin-rotation constants in stannous monoxide, SnO, and a new multi-isotopomer analysis

A Fourier transform microwave spectrometer has been used to make high resolution measurements on the J = 1-0 rotational transition for 11 isotopomers of SnO. For the most abundant isotopomer the transition was observed in the v = 0, 1, 2, and 3 states. Magnetic hyperfine structure was observed in the transitions for ¹¹⁵Sn¹⁶O, ¹¹⁷Sn¹⁶O and ¹¹⁹Sn¹⁶O. The nuclear spin-rotation constant C_I(Sn) has been determined for these isotopomers for the first time and these constants have been related to nmr shielding parameters. A multi-isotopomer analysis, including data from the ¹²⁰Sn¹⁷O and ¹²⁰Sn¹⁸O isotopomers, has been performed on the data. Born-Oppenheimer breakdown parameters were required in the fit and these parameters have been compared to those for the other Sn-chalcogenides.     

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.     

Global modelling of the experimental energy levels and observed line positions: Dunham coefficients for the ground state of 14N16O

ABSTRACT

A global treatment of the available experimental data of infrared transitions, far infrared transitions, and microwave transitions of 38 vibration-rotation bands for the ground state of ¹⁴N¹⁶O molecule was carried out. In the analysis, a global model with vibrational dependences of the parameters of the effective Hamiltonian for the diatomic molecule in ²Π electronic state was used. As a result of the fit, a set of the ‘Dunham-type’ molecular parameters was obtained. They reproduce the dataset of the experimental energy levels with experimental precision. The found set of the parameters was compared with the previous set determined by C. Amiot.     

Millimeter- and Submillimeter-Wave Spectra of CD2F2

The millimeter- and submillimeter-wave spectrum of ¹³CD₂F₂ present in natural abundance in methylene fluoride-d₂ (CD₂F₂) has been measured in the region 230-380 GHz. The spectrum was recorded using a frequency-modulated millimeter- and submillimeter-wave spectrometer. More than 200 rotational transitions in the ground state of ¹³CD₂F₂ with J≤45 and K_a≤8 have been assigned. A combined weighted least squares fit of the newly assigned transitions with previously reported microwave data has been carried out in the Watson's A- and S-reduced Hamiltonian. The data have been fitted with a standard deviation approaching the experimental accuracy, to provide improved values for the rotational and quartic centrifugal distortion constants, including sextic distortion constants for the ground state of ¹³CD₂F₂.     

Microwave spectrum of chloromethyl methyl ether

The microwave spectrum of chloromethyl methyl ether has been studied in the region 12.4–40 GHz. For ³⁵Cl species, a- and c-type transitions have been assigned for the ground state, the first excited state of the chloromethyl torsional mode, and the first excited state of the methyl torsional mode. Assignments were also made for the ground state of ³⁷Cl species. The assigned transitions are due to the gauche conformer. The nuclear quadrupole coupling constants were determined for the ground state of ³⁵Cl and ³⁷Cl species. The observed A-E splittings of the rotational transitions arising from the three vibrational states indicate a strong coupling between the two torsional vibrations. A model calculation based on the Hamiltonian previously used by Butcher and Wilson (J. Chem. Phys.40, 1671 (1964)), was carried out to account for the splittings and the vibrational frequencies of the two torsional modes. The barrier to internal rotation of the methyl group is estimated to be V₃ = 647 ± 17 cm^?1 (1.84 ± 0.05 kcal/mole).     

Microwave spectra of the ground vibrational state of formaldehyde substituted with O and O

Pure rotational transitions in the ground vibrational state have been measured for H₂¹²C¹⁸O, H₂¹²C¹⁷O, H₂¹³C¹⁸O, and H₂¹³C¹⁷O in the frequency region 8–75 GHz. These have included both Q- and R-branch transitions, and have permitted accurate evaluation of rotational constants and several quartic centrifugal distortion constants for each species. These in turn have permitted the prediction of several transitions of possible use in radioastronomy.     

12C16O18O: Analysis of rovibrational transitions Ov′2v3 → Ov′2(v3 − 1) (v2 = 0 and 1) observed in high-resolution emission spectra in the 4.5-μm region

Emission spectra of six isotopic species of CO₂ excited by dc discharge were recorded under Doppler limited resolution using the Fourier transform spectrometer of the Laboratoire d'Infrarouge in the 4.5-μm region. In this paper, the results concerning ¹²C¹⁶O¹⁸O are given. The band centers and the spectroscopic constants for 19 levels involved in vibrational transitions Δv₃ = 1 are reported. They reproduce 853 experimental wavenumbers with a RMS of the order of 2 × 10^?5 cm^?1 for the best vibrational transition, less than 1 × 10^?4 cm^?1 for most of the others. From experimental wavenumbers, to determine molecular parameters, it is shown that it is impossible to include in the same fit all the transitions Σ-Σ until v₃ = 10 using a polynomial representation of the rovibrational energy, the responsible phenomenon being the small Fermi resonance which occurs on Σ levels. Nevertheless, the 321 wavenumbers belonging to the first four vibrational transitions are satisfactorily reproduced by the model.     

N2Broadening in theCO 2–0 Band around 4167 cm

N₂broadening coefficients have been measured for 65 lines of the¹³C¹⁶O 2–0 band using a Fourier transform spectrometer. These lines are located in the spectral range 4011–4252 cm⁻¹. The spectra were recorded with 99% isotopically pure¹³CO in a White-type cell at a resolution of 0.005 cm⁻¹. Voigt profiles convolved with the FTS apparatus function were fitted to the experimental lineshapes using a nonlinear least-squares fit technique. From the fits the Lorentzian HWHM was determined as function of N₂pressure. Pressure broadening coefficients formbetween −33 and +34 were obtained with uncertainties of 5.8%. The results are compared to earlier published N₂broadening coefficients and our measurements in the 2–0 band of¹²C¹⁶O. To our knowledge this is the first investigation of¹³CO pressure broadening.