Sextic Distortion Constants Research Articles

The far-infrared spectrum of fluoroform (CHF 3)

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 pure rotational spectrum of diazomethane, H 2CNN, in the millimeter wave region

The rotational spectrum of diazomethane, H 2CNN, was investigated in the frequency range 100 to 400 GHz. Due to the C 2 v symmetry of the molecule, which is planar, only a-type dipole transitions were observed. The measurements were analyzed using Watson's S-reduced Hamiltonian. A detailed centrifugal distortion analysis yielded the following rotational and quartic centrifugal distortion constants: A = 272 979.1(8.1) MHz, B = 11 305.42697(45) MHz, C = 10 845.22028(47) MHz, D J = 4.14620(74) kHz, D JK = 396.817(92) kHz, D K = 22.0 MHz (fixed), d 1 = −192.55(42) kHz, d 2 = −57.27(39) Hz. Some sextic and higher-order distortion constants were determined and are discussed.

Higher-order centrifugal distortion effects in ONCl

One hundred and nine new rotational transitions of ONCl in the ground vibrational state have been measured. A centrifugal distortion analysis of these transitions yields the values of six sextic and one octic centrifugal distortion constants. A comparison between experimental and calculated sextic distortion constants is reported.

The Q-branch rotational spectrum in the ground state of CD4, studied by laser–rf double resonance spectroscopy

Near coincidences between CO2 and N2O laser lines and transitions in the n2 and n4 infrared bands of CD4 have been investigated using laser–rf double resonance spectroscopy. Six rf transitions have been assigned to ground state DJ = 0 rotational transitions of CD4, with J values of 7, 7, 10, 19, 19, and 21. A least squares fit of the observations using quartic and sextic tensor distortion constants only yields the parameters Dt = 32649.7±1.7 Hz, H4t = −1.9747±0.0044 Hz, and H6t = 1.1027±0.0016 Hz.

The harmonic force fields of methylene chloride and dichlorosilane from combined microwave and infrared data

The harmonic force fields of methylene chloride and dichlorosilane have been obtained by combining the vibrational wavenumbers and centrifugal distortion constants of several isotopic species. Although enough data were available from earlier work for dichlorosilane, it was first necessary for methylene chloride to determine its distortion constants from microwave spectra. Transitions were measured up to J = 80 and J = 90 for CH 2Cl 2 and CD 2Cl 2, respectively, and the analysis gave accurate rotational constants, and quartic and sextic distortion constants. Ground-state effective, substitution, ground-state average and approximate equilibrium structures have been obtained for both molecules.

Absorption spectrum of deuterated hydrazoic acid, D14N3 in the microwave and millimeterwave regiont

Thirty b-type P, Q and R branch rotational transitions and nineteen a-type Q and R branch transitions have been detected and measured for the slightly asymmetric rotor molecule D14N3 in the frequency range from 8 to 340 GHz. The information obtained from the analysis of the observed frequencies are greatly improved values of the K-dependent parameters AO = 344746.589(64) MHz, and DK = 92.242(33) MHz, refined values for the rotational constants BO and CO, a complete set of quartic centrifugal distortion constants and several sextic distortion constants. Both a and b components of the electric dipole moment were determined giving a total dipole moment of μ = 1.76(5) debye.

Microwave spectrum of CHD 2CN and CHD 2NC, and the harmonic force field and rz structure of methyl cyanide and isocyanide

The microwave spectra of CHD 2CN and CHD 2NC 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 r S 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.

The microwave centrifugal distortion moment spectrum of 16OPF 3

The microwave centrifugal distortion moment spectrum of the symmetric top 16O 31P 19P 3 in its ground vibronic state has been studied between 9 and 18 GHz with a Stark modulated spectrometer of high sensitivity. The frequencies of 152 transitions obeying the selection rules ΔJ = 0, ΔK = ±3 have been measured. A unique identification of the lines has been made by using the current results in a reanalysis of the allowed R-branch spectrum reported recently. From the Q-branch data, values were obtained for the rotational constant difference ( A 0 - B 0), two quartic distortion constants and three sextic distortion constants. In kHz, these are: ( A 0 - B 0) = 217,495 ± 2; D JK = (1.2971 ± 0.0007); D K = −(1.114 ± 0.012); H JK = (9.10 ± 0.27) × 10 −6; H KJ = −(6.8 ± 0.8) × 10 −6; H K = −(73 ± 30) × 10 −6. The value of ( A 0 - B 0) has been combined with the R-branch values of B 0 for 16OPF 3 and 18OPF 3 to give improved structural parameters. By comparing the intensities of two phosphoryl fluoride lines with the intensities of two silane lines of matching frequencies, the distortion dipole moment of 16OPF 3 has been determined to be (4.0 ± 1.4) × 10 −6 D.

The microwave spectrum of CHD 2Cl

The ground vibrational state microwave spectrum of CHD 2Cl has been studied in the region 26.5–40.0 GHz. From the observation of weak c-type transitions the A 0 rotational constants of CHD 2 35Cl and CHD 2 37Cl have been determined to be 95 426.08 ± 0.06 and 95 425.23 ± 0.11 MHz, respectively. The observed a-type and c-type transitions have been used to obtain A, B, C, all five quartic and one sextic distortion constants present in the reduced Hamiltonian of Watson for the 35Cl and 37Cl isotopic modifications of CHD 2Cl.

A planarity relation for sextic centrifugal distortion constants

The relations between the molecular parameters of a planar molecule are used to derive a planarity relation for the sextic centrifugal distortion constants from the recently published expressions [Aliev and Watson, J. Mol. Spectrosc. 61, 29 (1976)]. This relation, which contains only the rotational constants and the quartic and sextic distortion constants, is strictly valid only for the equilibrium constants, but will be useful as a constraint in the fitting of rotational energies if the experimental error is larger than the vibrational defect. The planarity relation is compared with the observed constants for the SO 2, O 3, NO 2, H 2O, and H 2S molecules. There appears to be a significant defect for SO 2 and for H 2O and its isotopes. The defect for SO 2 may be too large to be genuine, and possibly results from truncation of the Hamiltonian at the sextic terms.

The microwave Q branch of the distortion moment spectrum of 13CH4

The distortion moment microwave spectrum of 13CH4 has been studied with a conventional Stark modulated instrument having a sensitivity of ∼1×10−11 cm−1. Six pure rotational Q branch transitions have been observed between 8 and 20 GHz. With the assumption that the three octic tensor distortion constants L4T, L6T, and L8T have the same values as in 12CH4, values have been obtained for the one quartic and two sextic tensor distortion constants. These are (in Hz) DT= (132 983.32±0.48); H4T=−(17.0026±0.0018); H6T= (11.1869±0.0011). The errors given here are the standard deviations obtained from the least squares analysis. The justification for the assumption is presented, and estimates are given for the absolute errors in DT, H4T, and H6T, as well as for the isotopic shifts in L4T, L6T, and L8T. The measured differences between the 13CH4 and 12CH4 values of DT, H4T, and H6T are discussed with reference to recent theoretical calculations. A method is given of using these differences to calculate the tensor energy splittings of 13CH4 from those previously published for 12CH4.

The distortion moment spectrum of 28SiH4: The microwave Q branch

Eleven pure rotational Q-branch transitions have been observed between 8 and 25 GHz in the distortion moment spectrum of 28SiH4. The spectrometer used was a conventional Stark-modulated instrument modified to have a sensitivity of ~1 × 10−11 cm−1. From the eleven frequencies, values have been determined for the single quartic tensor distortion constant DT, the two sextic constants H4T and H6T, and the three octic constants L4T, H6T, and L8T. These are (in Hz): DT = (74 751.4 ± 1.6); H4T = −(6.044 ± 0.010); H6T = (2.598 ± 0.003); L4T = (46.5 ± 1.5) × 10−5; L6T = −(37.9 ± 0.8) × 10−5; L8T = −(76.6 ± 2.1) × 10−5. The errors here are the standard deviations obtained from a least squares analysis; estimates are also given of the absolute errors. For possible application in other high resolution studies of silane, the constants have been used to calculate all Q-branch splittings for J ≤ 20. The present results are compared to those obtained by double resonance methods by Kreiner and Oka; a definite identification has been found for one of their lines which had previously been tentatively assigned to another transition. The combination-differences data of Pierre, Guelachvili, and Amiot have been reanalysed on the basis of the current results to obtain improved values of the rotational constant and the quartic and sextic scalar distortion constants.

Calculated sextic centrifugal distortion constants of polyatomic molecules

By a perturbation treatment of the vibration-rotation Hamiltonian, expressions are derived for the sextic centrifugal distortion constants of a polyatomic molecule in terms of the basic molecular parameters. The calculation can be simplified by reordering the terms in the perturbation expansion. The theoretical expressions for the sextic distortion constants contain the cubic anharmonic potential constants, for which they are a possible source of information. The formulas are applied to molecules of various types of symmetry, and numerical results are computed for sulfur dioxide, ammonia and methane from published anharmonic force fields. The agreement with the observed distortion constants is good for SO 2 and reasonable for NH 3, but poor for CH 4. These results probably reflect the present state of knowledge of the cubic potentials of these three molecules.

ChemInform Abstract: MICROWAVE SPECTRA AND CENTRIFUGAL DISTORTION CONSTANTS OF OXETANE

Abstract 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 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- d 2 and the αα′- d 4 species, about 300 lines have been assigned for each molecule, and for the d 6 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.

Sextic centrifugal distortion constants of axially symmetric molecules

Expressions in terms of molecular parameters are obtained for the sextic centrifugal distortion constants H J , H JK , H KJ , and H K of axially symmetric molecules. A numerical example for the NH 3 molecule is given which shows that the sextic distortion of NH 3 is normal. It is emphasized that the observed sextic distortion constants provide additional information on the cubic anharmonic potential coefficients.

ChemInform Abstract: THE MICROWAVE SPECTRUM AND CENTRIFUGAL DISTORTION CONSTANTS OF VINYL CYANIDE

Chemischer InformationsdienstVolume 4, Issue 52 Physical Organic Chemistry ChemInform Abstract: THE MICROWAVE SPECTRUM AND CENTRIFUGAL DISTORTION CONSTANTS OF VINYL CYANIDE M. C. L. GERRY, M. C. L. GERRYSearch for more papers by this authorGISBERT WINNEWISSER, GISBERT WINNEWISSERSearch for more papers by this author M. C. L. GERRY, M. C. L. GERRYSearch for more papers by this authorGISBERT WINNEWISSER, GISBERT WINNEWISSERSearch for more papers by this author First published: December 25, 1973 https://doi.org/10.1002/chin.197352086AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume4, Issue52December 25, 1973 RelatedInformation

The microwave spectrum and centrifugal distortion constants of vinyl cyanide

The rotational spectrum of the ground state of vinyl cyanide has been assigned and measured in the frequency regions 8–37 GHz and 90–200 GHz. A total of 140 transitions has been measured and assigned to quantum numbers as high as J = 35 and K = 12. These new measurements have been used to calculate accurate values for all the rotational and quartic centrifugal distortion constants and some sextic distortion constants. The rotational constants are in MHz: A ̃ = 49850.700 ± 0.013 ; B ̃ = 4971.2141 ± 0.0008 ; C ̃ = 4513.8289 ± 0.0008 .