The microwave spectra of PH2D and PHD2, and the harmonic force field and structure of phosphine

Measurements of the pure rotational spectra of PH₂D and PHD₂ have been extended to include new Q-branch transitions and R-branch transitions. The rotational constants have been independently evaluated for the first time, along with some quartic and sextic centrifugal distortion constants. The spectrum of PD₃ has been reanalyzed to make the constants consistent with those reported for PH₃. The new results have been incorporated in a harmonic force field analysis. Both ground state average (r₂) and equilibrium (r_e) structures have been estimated.     

Microwave spectra and centrifugal distortion constants of oxetane

The microwave spectra of oxetane (trimethylene oxide) and its three symmetrically deuterated isotopic species have been observed on a Hewlett-Packard microwave spectrometer from 26.5 to 40 GHz. For the parent species, the β-d₂ and the αα′-d₄ species, about 300 lines have been assigned for each molecule, and for the d₆ species more than 600 lines have been assigned. The assignments range from v = 0 to v = 5 in the puckering vibration; although they are mostly Q transitions, either 3 or 4 R transitions have been observed for each vibrational state.The spectra have been interpreted using an effective rotational hamiltonian for each vibrational state, including five quartic distortion constants according to Watson's formulation, and a variable number of sextic distortion constants; in general, the lines are fitted to about ± 10 kHz. The distortion constants show an anomalous zig-zag dependence on the puckering vibrational quantum number, similar to that first observed for the rotational constants by Gwinn and coworkers. This is interpreted according to a simple modification of the standard theory of centrifugal distortion, involving the double minimum potential function in the puckering coordinate.     

Microwave spectrum of CHD2CN and CHD2NC,and the harmonic force field and rz structure of methyl cyanide and isocyanide

The microwave spectra of CHD₂CN and CHD₂NC have been measured from 18 to 40 GHz; about 20 type A and 30 type C transitions have been observed for each molecule. These have been fitted to a Hamiltonian using 3 rotational constants, and 5 quartic and 4 sextic distortion constants, in the I^rS reduction of Watson [in “Vibrational spectra and structure” Vol. 6 (1977)]; the standard error of the fit is 26 kHz. For methyl cyanide the 5 quartic distortion constants have been used to further refine the recent harmonic force field of Duncan et al. [J. Mol. Spectrosc.69, 123 (1978)], but the changes are small. Finally, for both molecules, the harmonic force field has been used to determine zero point average moments of inertia I_z from the ground state rotational constants for many isotopic species, and these have been used to determine an r_z structure. The results are compared with r_s structure calculations.     

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.     

Centrifugal distortion analysis of pure rotational spectra of H216O,H217O,and H218O

Centrifugal distortion analyses based entirely on high-quality infrared data are carried out for the ground vibrational states of H₂¹⁶O, H₂¹⁷O, and H₂¹⁸O. As a result of the analyses, the values of 27 rotation and distortion constants for each species are determined. By using these constants it was possible to improve considerably the accuracy of the literature values for rotational energy levels at high J_τ, especially for H₂¹⁷O and H₂¹⁸O. The experimental values for the energy levels are deduced from the observed rotational transitions constituting the fitted data.     

The pure rotational spectra of the lanthanum monohalides, LaF, LaCl, LaBr, LaI

Pure rotational spectra have been measured for all the major isotopomers of the lanthanum monohalides, LaF, LaCl, LaBr, and LaI, in their ground and (except for ) excited vibrational states. The spectra were observed with a cavity pulsed jet Fourier transform microwave spectrometer in the frequency range 5-24 GHz. The molecules were prepared by laser ablation of La metal and allowing the resulting plasma to react with SF₆, Cl₂, Br₂, or CH₃I precursor in an Ar carrier gas of the pulsed jet. For LaBr this is the first reported spectrum of any kind. Rotational constants, centrifugal distortion constants, nuclear quadrupole coupling constants, and nuclear spin-rotation constants have been determined for all the molecules. Accurate equilibrium (r_e) internuclear distances have given an indication of where the Born-Oppenheimer approximation is beginning to fail. From the centrifugal distortion constants and vibration-rotation (α_e) constants good estimates of the harmonic vibration frequencies and bond dissociation energies have been obtained. The halogen nuclear quadrupole coupling constants indicate the molecules to be highly ionic.     

Ritz assignment and Watson fits of the high-resolution ring-puckering spectrum of oxetane

Oxetane is a four-membered ring molecule exhibiting a large-amplitude ring-puckering motion. In order to analyze this vibration we recorded a rotationally resolved far-infrared spectrum between 50 and 145 cm⁻¹. The analysis of the ring-puckering fundamental band with the assignment of 1108 lines, has been presented in a previous paper. In the present work we present a list of further 6531 assigned transitions between the five lowest excited ring-puckering states. The 4983 term values involved in the transitions assigned in this and in the preceding work have been evaluated by the “Ritz” program, and are now available. An A-reduced Watson Hamiltonian in any of the three representations I^r, II^r, and III^r was used to perform a fit of the assigned transitions. Precise rotational constants and quartic as well as a full set of sextic centrifugal distortion constants were obtained for the investigated ring-puckering states. For the first time, high-resolution values for the vibrational G_v parameters have been obtained, and we have added terms in x⁶ and x⁸ to the double minimum-potential well describing the ring-puckering motion, in order to reproduce their values within the experimental accuracy. The same potential still reproduces the lower resolution values of the Q-branch origins involving higher ring-puckering states up to v_rp=14 found in the previous literature.     

Microwave spectra of SiH2DF and SiHD2F: Harmonic force field and molecular structure

The ground vibrational state rotational spectrum of SiH₂DF and SiHD₂F has been studied in the frequency region 24–58 GHz. The observed transitions have been used to obtain the A, B, C rotational constants and three of the five quartic distortion constants present in the reduced Hamiltonian of Watson.The A, B, C rotational constants obtained in this work in combination with the B constants of the six symmetric isotopes were used to determine accurate substitution and average structures. An approximate equilibrium structure is also estimated.The general harmonic force field of silyl fluoride has been redetermined using all existing data.     

Rotational spectra of isotopic di-thioformic acids with a structure of trans HCSSH: Ab initio estimates of cis/trans structures,energies, dipole moments,and torsional barrier

Microwave transitions (18.6–40 GHz) of ground-level trans HC³⁴S³²SH, HC³²S³⁴SH, HC³²S³²S²H and of cis HC³²S³²S²H have been observed and assigned. Rotational and distortion constants have been calculated. These data with earlier data for trans/cis HC³²S³²SH are not sufficient to fix an r_s or r₀ structure for trans HCSSH. Instead, an “iterative” structure of trans HCSSH has been derived making full use of all data obtained for isotopic trans species. An ab initio estimate of the geometry of trans HCSSH agrees with the iterative structure within expectation. This also holds for the calculated energy difference ?(cis) - ?(trans) and for calculated dipole moment components μ_a along the a axis of least moment of inertia.     

The microwave spectrum of cyanophosphaacetylene, H2PCCCN

The a type transitions of the microwave rotational spectra of cyanophosphaacetylene, H₂PCCCN, have been investigated in the frequency region between 5 and 26.5 GHz by Fourier transformation microwave (FTMW) spectroscopy. Rotational, centrifugal distortion and ¹⁴N nuclear quadrupole coupling constants have been determined. Density functional theory level ab initio calculations were performed to predict the molecular constants, and the predicted values are in good agreement with our experimentally determined results. The ¹³C and ¹⁵N isotopomer transitions were also observed. The derived r₀ structure is quite comparable to the calculated H₂PCCCN equilibrium geometry.     

Microwave spectra of the ground vibrational state of formaldehyde substituted with 17O and 18O

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.     

Microwave and submillimeterwave spectra of CH2DI and CHD2I

The pure rotational spectra of CH₂DI and CHD₂I have been measured by microwave Fourier transform spectroscopy, millimeterwave spectroscopy and submillimeterwave spectroscopy. The quadrupole hyperfine structure due to iodine has been analyzed by direct diagonalization of the quadrupole tensor. For the J = 1-0 transition of the ground state of CH₂DI, the quadrupole hyperfine structure due to deuterium could be resolved and the quadrupole coupling constant eQq_aa(D) determined.Accurate rotational and centrifugal distortion constants (up to sextic terms) have been determined. They are compared to the constants derived from the ground state combination differences (GSCD). A good agreement is observed but it is also found that the two kinds of data (GSCD and microwave) are complementary and a combined fit allows us to significantly improve the accuracy of the constants.     

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.     

Observation and analysis of fundamental bending mode of T2O

The absorption spectrum of the ν₂ band of T₂O vapor has been observed at 0.04 cm^?1 resolution. A total of 549 transitions has been assigned; 474 of these have been used to evaluate the rotational constants A, B, and C as well as the fourth-order and sixth-order distortion constants and one eighth-order constant for the upper vibrational state.     

Pure rotational spectra of allene-1, 1-d2 and allene-d1 observed by microwave Fourier transform spectroscopy

Pure rotational transitions of allene-1, 1-d₂ and allene-d₁ in their vibronic ground state have been observed with a pulsed microwave Fourier transform spectrometer for the 8- to 18-GHz frequency range. Thirteen new transitions of allene-1, 1-d₂ with J up to 32 have been assigned. The measured transition frequencies have been combined with earlier measurements of Hirota and Matsumura [J. Chem. Phys. 59, 3038–3042 (1973)] in a least-squares fit of the rotational constants B and C and the centrifugal distortion constants Δ_J, Δ_JK, δ_J, and δ_K. Fifteen transition of allene-d₁ with J up to 34 have been assigned. The rotational constants A, B, and C, and the quartic centrifugal distortion constants Δ_J, Δ_JK, Δ_K, δ_J, and δ_K have been determined from the measured frequencies in a least-squares fit.     

Identification of forbidden vibration-rotation transitions in 15NH3

Forbidden Δ|k ? l| = 3 vibration-rotation transitions have been observed in the ν₄ band of ¹⁵NH₃. The analysis of these transitions, together with previously published data on the allowed transitions, has made it possible to determine a set of molecular parameters, including for the first time the rotational constant C as well as the centrifugal distortion constants D_K and H_KKK, which are necessary for the calculation of energy levels. Some weak forbidden transitions in the ν₂ band have also been observed.     

The υ1 fundamental bands of trans- and cis-DONO studied by high-resolution Fourier-transform spectroscopy

The absorption spectrum of deuterated nitrous acid DONO in the region from 2350 to 3000 cm⁻¹ has been recorded at a resolution of 0.003 cm⁻¹ using a Fourier-transform spectrometer. For the first time, 1366 a- and b-type transitions in the υ₁ fundamental band of trans-DONO and 741 b-type transitions in the υ₁ fundamental band of cis-DONO have been assigned. Rotational and centrifugal distortion constants up to sextic order were determined for the v₁ = 1 states of trans- and cis-DONO using non-linear least-squares calculations. Synthetic spectra calculated using the new rovibrational constants obtained for both species reproduce the observed spectra very well. In addition, the infrared transitions of this study were used, together with previously published pure rotational transitions, to determine improved rotational and centrifugal distortion constants of the ground states of trans- and cis-DONO.     

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.     

The far-infrared spectrum of fluoroform (CHF3)

The far-infrared spectrum of fluoroform has been recorded in the region between 7 and 60 cm⁻¹ at a resolution of 0.002 cm⁻¹. More than 1400 rotational transitions in the ground state have been measured and assigned up to J″ = 80. Simultaneous analyses of these measurements and of microwave and millimeter-wave data reported previously have been performed. Improved values of the ground state rotational and centrifugal distortion constants, including the sextic distortion constants reported for the first time, have been obtained. Rotational transitions in a few low-lying vibrational states have also been observed.     

The microwave spectrum of the pyramidal isomer of disulfur difluoride: SSF2

The pyramidal isomer of disulfur difluoride, SSF₂, has been prepared by passing gaseous disulfur dichloride through heated potassium fluoride. The microwave spectra of three isotopic species of SSF₂ have been measured in the 26- to 76-GHz frequency region. For the most abundant isotopic species transitions with J values up to 79 have been observed. These data have been combined with previous measurements of low-J lines by R. L. Kuczkowski [J. Amer. Chem. Soc. 86, 3617–3621 (1964)] and fit to obtain values for the rotational constants and centrifugal distortion constants. The quartic centrifugal distortion constants have been used together with existing vibrational data to determine an harmonic force field for the molecule. Finally, ground state average and equilibrium structures have been calculated for SSF₂.