Ground-state Rotational Spectra Research Articles

The ground state rotational spectrum of H 2Se: Weighted microwave-infrared analysis

Ninety-four transitions of the five major species of hydrogen sulfide have been measured in the 100–600 GHz region of the microwave spectrum. These data have been combined with infrared data for the calculation of the energy levels and spectral constants of the several species. The data in both spectral regions can be fitted to within expected experimental error by means of Watson's reduced centrifugal distortion Hamiltonian. The rotational and P 4 distortion parameters are for H 2 80Se (in MHz): a = 244 099.89 ± 0.29, B = 232 561.95 ± 0.29, C = 116 874.93 ± 1.76, Δ J = 34.950 ± 0.03, Δ JK = −118.189 ± 0.07, Δ K = 88.1873 ± 0.13, δ J = −2.12091 ± 0.012, δ K = 461.0394 ± 1.0.

Microwave Spectrum and Barrier to Internal Rotation of 5-Methylisoxazole

Abstract The ground state rotational spectrum of 5-methylisoxazole has been studied in the region 18 000 -36 000 MHz. The A and E state transitions have been assigned. The rotational constants are A = 9230.831 MHz, B = 3559.334 MHz and C = 2610.255 MHz and the three-fold barrier to internal rotation of the methyl group was calculated to be 777.2 ± 5.5 cal mol-1 .

ChemInform Abstract: METHYL GROUP TILT AND STRUCTURE FROM ROTATIONAL SPECTRA OF THE CH2DNHCL MONODEUTERATED SPECIES

Abstract The structure and tilt of the methyl group of CH3NHCl have been determined by analysis of the three different ground state rotational spectra of the methyl monodeuterated species. The tilt was found to be ⋍3.5° which is of the same order of magnitude and towards the unshared pair of electrons at the nitrogen atom as in methylamine and its derivatives. The barrier to internal rotation was determined form the A-E splittings of the previously measured transitions and found to be 3781 ± 14 cal/mole for CH3NHCl and 3784 ± 15 cal/mole for CH3NDCl, while the values obtained under the assumptions of no tilt and of asymmetric methyl group as in methylamine were 3707 ± 30 cal/mole for CH3NHCl and 3726 ± 25 cal/mole for CH3NDCl. Some information has also been deduced on the orientation of the z axis of the principal quadrupole coupling tensor.

A comparison between shell-model configuration mixing calculations and the MCHF model in the ground state rotational spectra of 20Ne, 22Ne and 24Mg

Shell-model and multi-configuration Hartree-Fock (MCHF) calculations in an Od 5 2 -1s 1 2 oscillator basis are compared for 20Ne, 22Ne and 24Mg. The similarity of the calculated results in the two models shows that the MCHF method is a very good approximation to the shell-model calculations.

The angular momentum dependence of correlations in the ground state rotational spectra of20Ne and22Ne

Multi-Configuration-Hartree-Fock (MCHF) calculations with angular momentum projection before the variation of the internal degrees of freedom have been performed for the nuclei20Ne and22Ne. This procedure yields different correlated intrinsic states for the different members of a rotational band. Thus the angular momentum dependence of correlations has been studied. Experimentally, the ground state spectra of20Ne and22Ne show properties similar to the phase transitions observed in some rare earth nuclei which have been well reproduced through the present calculations. The calculated spectra andBE2-values show a significant improvement compared to the ones obtained by variation before the angular momentum projection is effected.

Methyl group tilt and structure from rotational spectra of the CH 2DNHCl monodeuterated species

The structure and tilt of the methyl group of CH 3NHCl have been determined by analysis of the three different ground state rotational spectra of the methyl monodeuterated species. The tilt was found to be ⋍3.5° which is of the same order of magnitude and towards the unshared pair of electrons at the nitrogen atom as in methylamine and its derivatives. The barrier to internal rotation was determined form the A- E splittings of the previously measured transitions and found to be 3781 ± 14 cal/mole for CH 3NHCl and 3784 ± 15 cal/mole for CH 3NDCl, while the values obtained under the assumptions of no tilt and of asymmetric methyl group as in methylamine were 3707 ± 30 cal/mole for CH 3NHCl and 3726 ± 25 cal/mole for CH 3NDCl. Some information has also been deduced on the orientation of the z axis of the principal quadrupole coupling tensor.

ChemInform Abstract: ROTATIONAL AND VIBRATIONAL SPECTRA OF 2‐FLUOROPROPANE

Chemischer InformationsdienstVolume 4, Issue 42 Physical Organic Chemistry ChemInform Abstract: ROTATIONAL AND VIBRATIONAL SPECTRA OF 2-FLUOROPROPANE JOHN H. GRIFFITHS, Search for more papers by this authorNOEL L. OWEN, Search for more papers by this authorJOHN SHERIDAN, Search for more papers by this author JOHN H. GRIFFITHS, Search for more papers by this authorNOEL L. OWEN, Search for more papers by this authorJOHN SHERIDAN, Search for more papers by this author First published: October 16, 1973 https://doi.org/10.1002/chin.197342071AboutPDF 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 onEmailFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume4, Issue42October 16, 1973 RelatedInformation

Pairing correlations and simultaneous projection of particle number and angular momentum in light nuclei

The Hartree-Bogolubov theory with simultaneous projection on sharp angular momentum quantum number and sharp particle number is presented as a description of the ground state rotational bands of doubly even nuclei. Calculations with effective G-matrix elements of the Hamada-Johnston potential and also of the Yale potential have been performed within this framework for the nuclei 20Ne, 22Ne, 24Ne, 24Mg, 26Mg, 28Si, 30Si, 32S and 34S. Rotational energies, moments of inertia, pairing correlations, quadrupole moments and B(E2) values are discussed and compared with available experimental data. The effect of particle number fluctuation on the ground state rotational spectrum and on the intrinsic wave function is investigated. The particle number projection turns out to be important for the description of the rotational levels, whereas it has only a negligible effect on the properties of the intrinsic wave function. Comparison with Hartree-Fock results and with experimental data shows that the inclusion of pairing correlations provides a significant improvement on the excitation energies, their relative ratios and the angular momentum dependence of the moments of inertia. All solutions show an antistretching effect in the quadrupole moments and especially in the B(E2) values. The rotational bands in 20Ne, 22Ne, 24Ne and 28Si turn out to be well described in the framework presented.

Microwave spectrum, structure and dipole moment of trimethylamine-borane

The ground state rotational spectra often isotopic species of trimethylamineborane, (CH 3) 3N 10BH 3, (CH 3) 3N 11BH 3, (CH 3) 3N 10BD 3, (CH 3) 3N 11BD 3, (CH 3) 3N 11BD 2H, (CD 3) 3N 10BH 3, (CD 3) 3N 11BH 3, (CD 3) 3N 10BD 3, (CD 3) 3N 11BD 3 and ( 13CH 3)( 12CH 3) 2N 11BH 3, have been measured and the effective moments of inertia obtained. The utilization of Kraitchman's equations leads to an r s value of the B-H distance of 1.211±0.003 Å and a NBH angle of 105.32±0.16°. By a least squares fit of the rotational constants the following structural parameters were obtained: r(NC) = 1.495 Å, r(BN) = 1.609 Å, and ∠BNC = 110.9°. The value of the dipole moment was found to be 4.59±0.13 D. A lower limit to the barrier to internal rotation of the BH 3 group was determined to be 3.4 kcal/mole.

Rotational and vibrational spectra of 2-fluoropropane

The infra-red and microwave spectra of 2-fluoropropane have been measured and analysed. From the ground state rotational spectrum the rotational constants were calculated to be A= 8693.82, B= 8102.51 and C= 4788.83 MHz. Analysis of rotational lines in the first torsional states (+) and (–) lead to a value for the internal rotation barrier of 14.9 ± 1.3 kJ mol–1(3560 ± 300 cal mol–1). No analysis of top–top coupling was made but these terms are estimated to be less than those found for propane. The dipole moment was found to be 1.96 ± 0.03 D. Many of the infra-red absorption lines have been assigned to characteristic group frequencies.

Millimeter Wave Rotational Spectrum of HSSH and DSSD. IV. P, Q, and R Branches of HSSH

The earlier microwave measurements on the ground-state rotational spectrum of HSSH have been extended into the submillimeter wave region to a wavelength of 0.7 mm, or 420 GHz, for the observation of the Q branch of the K=2← 1 rotational subband. In the lower-frequency range 50–200 GHz, various Q-, R-, and P-branch transitions have also been assigned. From these measurements the ground-state rotational constants are (in megahertz): A=146 858.170± 0.032, B=6 970.430± 0.003, C=6 967.689± 0.003, which yield an asymmetry parameter bp=−0.98× 10−5 or κ =−0.999960. The most remarkable feature of the perpendicular-type spectrum is the anomalous splitting of the K=2 energy levels. It is found that the splitting of the K=2 levels is not only one order of magnitude larger than that expected from the small asymmetry of the molecule, but also that the sequence of these levels is reversed as compared to their ``normal'' order, determined by the asymmetry splitting. These anomalies are explained as in paper II of this series by the additional K-type doubling (centrifugal-distortion splitting) caused by the centrifugal-distortion operator (Ĵ+4+Ĵ−4) in the rotational Hamiltonian. Unlike DSSD, the centrifugal-distortion splitting in HSSH is nearly masked by the larger asymmetry splitting.

Microwave Spectrum of Methylbromodiazirine

Ground-state rotational spectra of CH379BrCN2 and CH381BrCN2 have been assigned, and a set of calculated r0 structural parameters are: r(NN) = 1.240 ± 0.005 Å, r(CBr) = 1.904 ± 0.02 Å, ∢CCBr = 116.5° ± 2.0°, and ∢CCN2 = 124.5 ± 2.0°. The Br quadrupole coupling constants (megahertz) for CH379BrCN2 are χaa = 539.8 ± 8.0, χbb = −279.4 ± 6.0, χcc = −260.4 ± 8.0 and for CH381BrCN2 are χaa = 451.1 ± 8.0, χbb = −232.3 ± 6.0, and χcc = −218.8 ± 8.0. A preliminary value for the barrier to internal rotation is 1.7 kcal mol−1.

Rotational Spectra of Substituted Diazirines. III. Methylchlorodiazirine

Ground-state rotational spectra of CH335ClCN2 and CH337ClCN2 have been assigned, and the derived r0 structural parameters are: r(NN) = 1.241 ± 0.005 Å, r(CCl) = 1.743 ± 0.01 Å, r(CC) = 1.498 ± 0.01 Å, ∢C–C–Cl = 116.7° ± 1.0°, ∢CCN2 = 124.5° ± 1.0°, and ∢NCN = 50.2° ± 0.5°. The internal-rotation splittings for CH335ClCN2 yield a barrier to internal rotation of 1689 ± 10 cal mole−1. The Cl quadrupole coupling constants (megahertz) for CH335ClCN2 are χaa = −66.51, χbb = 32.91, χcc = 33.60 and for CH337ClCN2 are χaa = −53.07, χbb = 26.40, χcc = 26.67. The nitrogen quadrupole splittings were generally unresolved.

Rotational Spectra of Substituted Diazirines. II. Methyldiazirine

Ground-state rotational spectra of HCH3CN2 and HCD3CN2 have been assigned, and the structural parameters obtained by least-squares fitting the observed moments are r(CN) = 1.481 ± 0.01 Å, r(CC) = 1.501 ± 0.01 Å, r(NN) = 1.235 ± 0.005 Å, and ∢N2CC = 122.3 ± 0.6°. The internal rotation splittings for HCH3CN2 and HCD3CN2 yield barriers of 773.9 and 770.4 ± 1.0 cal/mole, respectively. The quadrupole coupling constants χaa, χbb, and χcc are + 0.48 ± 0.8, − 2.53 ± 0.4, and + 2.05 ± 0.4 MHz for HCH3CN2 and 0.20 ± 0.8, − 2.36 ± 0.4, and + 2.16 ± 0.4 MHz for HCD3CN2. Analysis of the Stark effect give a dipole moment of 2.03 ± 0.07 D for HCH3CN2 and 2.02 ± 0.07 D for HCD3CN2.

Rotational spectrum of ethylene episulfoxide

The ground state rotational spectrum of ethylene episulfoxide agrees with NMR and Raman data in predicting a molecule with C s symmetry. The dipole moment is 3.66 D.

Rotational Spectra of Substituted Diazirines. I. Dimethyldiazirine

Ground-state rotational spectra of (CH3)2CN2 and (CD3)2CN2 have been assigned, and the derived structural parameters are: r(NN) = 1.235 ± 0.005 Å, r(CC) = 1.499 ± 0.01 Å, r(CN) = 1.490 ± 0.01 Å, ∢C–C–C = 119.7 ± 0.5°. The internal rotation splittings for (CH3)2CN2 yield a barrier to internal rotation of 1129 ± 20 cal mole−1 and an angle of 120.4 ± 0.4° between the top axes. For (CH3)2CN2 the quadrupole coupling constants (MHz) are χaa = −0.94 ± 0.8, χbb = 3.20 ± 0.4, and χcc = −2.27 ± 0.4, while for (CD3)2CN2 χaa = −1.21 ± 0.8, χbb = 3.44 ± 0.4, and χcc = −2.23 ± 0.4. Analysis of the Stark effect gave a dipole moment of 2.19 ± 0.07 D.

Microwave Spectrum, Ring-Puckering Potential Function, Ring Structure, and Dipole Moment of Cyclobutanone

The microwave spectrum of cyclobutanone in the ground state and the first 10 excited states of the ring-puckering vibration has been assigned. Most features of the observed variation of rotational constants with ring-puckering state and of the far-infrared spectrum are accounted for with the ring-puckering potential function V(Z) = ν0[12Z2 + 0.4918Z4 + 1.598 exp(−1.0Z2)], with ν0 = 29.85 cm−1. Z is a dimensionless coordinate for the ring-puckering motion. A barrier of 7.6 ± 2 cm− exists at the planar ring conformation; with the υ = 0 level lying 9.2 cm−1 above the top of the barrier. A perturbation of the υ = 8 state is discussed. The ground-state rotational spectra of the three 13C monosubstituted species have also been assigned and the structure of the ring determined. With the carbonyl carbon labeled C1 and other carbons numbered sequentially around the ring, the ring structural parameters are r(C1C2) = 1.527 + 0.003 Å, r(C2C3) = 1.556 ± 0.001 Å, ∠C2C1C2′ = 93.1 ± 0.3°, ∠C1C2C3 = 88.0 ± 0.3°, ∠C2C3C2′ = 90.9 ± 0.2°. Stark-effect measurements have yielded a value of 2.89 ± 0.03 D for the dipole moment of the common isotopic species in the ground vibrational state.

Microwave spectrum, dipole moment, structure, and internal rotation of dimethyl selenide

The microwave spectra of five isotopic species of dimethyl selenide are reported. Changes in rotational constants with isotopic substitution yield the following structural parameters: CSe 1.943 A ̊ <CSeC 96°11′ CH 1.093 A ̊ <HCH 110°18′ 2θ 100°7′ where 2 θ is the angle between the symmetry axes of the methyl groups. From Stark effect measurements the dipole moment of dimethyl selenide is found to be 1.41 ± 0.02 debye. The fine structure in the ground-state rotational spectrum of all five isotopic species has been resolved and analyzed. This fine structure results from coupling of internal and overall rotation. The height of the potential barrier hindering internal rotation has been determined as 1500 ± 20 cal/mole.

Centrifugal Distortion Effects in Asymmetric Rotor Molecules. I. Quadratic Potential Constants and Average Structure of Oxygen Difluoride from the Ground-State Rotational Spectrum

The microwave spectrum of oxygen difluoride has been thoroughly investigated in the frequency regions 8 to 40 and 49 to 60 kMc. A total of 83 absorption lines have been assigned as ground-state rotational transitions in which the total angular momentum J ranges from 1 to 39. These data provide the means for a critical test of the Kivelson—Wilson theory of centrifugal distortion. It is found that the K—W energy expression only approximately accounts for the measurements. The K—W formula obtains when (1) separation of rotation and vibration is carried out to second-order of approximation, and (2) when the quartic (P4) distortion terms in the resulting effective rotational Hamiltonian are treated by first-order perturbation theory. It is found that both of these approximations must be carried one order higher to obtain a satisfactory fit of the observed rotational frequencies of OF2. Analysis of the rotational spectrum by the method of least squares yields the following ground-state rotational parameters (Mc): A=58782.630, B=10896.431, C=9167.412, τxxxx=—0.0949559, τzzzz=—6.615402, τxxzz=0.399611, τxzxz=—0.162486, HJK=—2.2184×10—6, and HKJ=3.1073×10—6, where HJK and HJK are the coefficients of semiempirical P6 distortion terms in the effective rotational Hamiltonian. The quartic distortion constants yield vibrational frequencies which agree with the observed values to within 4% or better. By combining microwave data with the observed vibrational frequencies the following quadratic potential constants are obtained: fr=3.9499 mdyn/Åfrr=0.8059 mdyn/Å,fα/r2=0.7237 mdyn/Å,frα/r=0.1373 mdyn/Å.Using this potential function with formulas derived by Laurie and Herschbach the average structure of OF2 in the ground vibrational state is found to be 〈r〉=1.4124 Å, 〈α〉=103∘10′,where r is the OF distance, and α the FOF angle.

Microwave Spectrum, Dipole Moment, Structure, and Internal Rotation of Dimethyl Sulfide

The microwave spectra of five isotopic species of dimethyl sulfide are reported. Changes in rotational constants with isotopic substitution yield the following structural parameters: CS 1.802 A; CSC=98°52′; CH 1.901 A; HCH=109°34′; 2θ=104°22′, where 2θ is the angle between the symmetry axes of the methyl groups. The equilibrium conformation of both methyl groups is the staggered one, i.e., staggered with respect to the adjacent CS bond axis. From Stark effect measurements the dipole moment of dimethyl sulfide is found to be 1.50±0.01 debye. Fine structure in the ground-state rotational spectrum of (CH3)2S and an excited torsional state of CH3SCD3 has been resolved and analyzed. This fine structure results from coupling of internal and over-all rotation and is affected by top-top coupling terms in the kinetic and potential energy portions of the Hamiltonian. Neglecting only the potential energy coupling terms, the (CH3)2S and CH3SCD3 splittings yield as the barrier to internal rotation 2132±6 and 2118±3 cal/mole, respectively. Estimates of the potential energy coupling parameters are made. They are found to be an order of magnitude smaller than the main term of ∼2100 cal/mole in the Fourier expansion of the potential energy.