Search

The highly sensitive method of radio-frequency-infrared double resonance inside a CO2 laser is applied to study collision-induced transitions in CH3I in a four-level double resonance scheme. Pure nuclear quadrupole resonances are observed as the result of collision population transfer between different rotational levels. The intensity ratios of the collision-induced dips to the corresponding three-level double resonance signals are measured for a number of transitions in the ground and excited vibrational states. Collision selection rules in the pure gas and in mixtures with polar and non-polar gases are discussed.

The rotational spectra of H 2 13 COH + and D 2 COD + were observed in the 110–224 GHz frequency region using a magnetically confined negative glow discharge as ion production source. Analysis of the spectra allowed determination of the ground state rotational and quartic centrifugal distortion constants. These new data, together with those of Dore et al. [ Chem. Phys. Lett. 244, 145 (1995)] concerning H 2 COH + , allow an estimate of the molecular structure of protonated formaldehyde.

Thirteen ground state rotational lines of protonated formaldehyde, H 2 COH + , were measured using a magnetically confined negative glow discharge as a production source. These new measurements together with those of Chomiak et al. [Can. J. Phys. 72 (1994) 1078] have allowed a refinement of the rotational parameters. The astrophysical aspects of previous and future searches of this ion are outlined.

A number of pure quadrupole resonances in the ground and v 4 = 1 states of AsH 3 have been measured using the radiofrequency-infrared double-resonance technique in a CO 2 laser cavity. The ground stale resonances were titled together with all available radiofrequency and microwave data using the standard treatment. Strong vibration-rotation interactions between the v 2 = 1 and v 4 = 1 states affect the observed spectrum in the v 4 = 1 state. The Hamiltonian model by Aliev and Hougen ( J. Mol. Spectrosc. 106, 110-123 (1984)) has been used, in the form of a computer program. to describe within the experimental uncertainties the new measurements in a combined analysis with all known experimental data in the v 2 = 1 and v 4 = 1 states.

The millimeter-wave spectrum of DNCCN + has been observed and analyzed. The values of the rotational constants are B 0 =4158.32201(49) MHz and D 0 =0.45089(19) kHz.

The two isotopic forms of stibine, 121 SbH 3 and 123 SbH 3 , have been spectroscopically studied with high resolution. Pure quadrupole resonances both in the ground and in the v 4 = 1 states have been observed using the infrared-radiofrequency double resonance technique in a CO 2 laser cavity. Characteristic hyperfine patterns resulting from direct l -type doubling transitions in the v 4 = 1 state have been measured by microwave spectroscopy. The hyperfine pattern in the ground state is reproduced following the standard treatment. Strong vibration-rotation interactions between the v 2 = 1 and v 4 = 1 states affect the observed spectrum in the v 4 = 1 state. A refined treatment of the vibration-rotation interactions between the hyperfine levels in this state was necessary in order to adequately analyze the experimental data. Quadrupole interaction parameters for a degenerate state of a symmetric-top molecule have been determined for the first time.

The high-resolution microwave spectrum of the axial conformer of cyclohexyl chloride has been assigned for both the Cl(35) and Cl(37) isotopic species, in natural abundance. Moreover, the high-resolution microwave spectrum of the equatorial conformer, previously assigned in the ground state [ Chem. Phys. Lett. 21 , 592–594 (1973)], has been further investigated. Several low-energy vibrational satellites have been studied for the Cl(35) isotopic species of both the axial and the equatorial isomers. The ground state centrifugal distortion constants for both the isotopic species of the two rotamers, and the quadrupole coupling constants of Cl(35) and Cl(37) axial isomer and of Cl(37) equatorial isomer (not reported previously) have been determined. From line relative intensity measurements the energy difference between the two conformers has been calculated to be 0.51 ± 0.15 kcal/mol, the equatorial isomer being more stable. In the same way, the vibrational energies of the investigated vibrational satellites have been computed. A structural model for axial cyclohexyl chloride is proposed on the basis of the available experimental data.

The microwave spectra of cyclohexyl bromide and cyclohexyl iodide have been investigated in the gas phase between 8 and 40 GHz. While for cyclohexyl bromide only low resolution spectra have been recorded, for cyclohexyl iodide high resolution spectra of both the equatorial and the axial isomer have been analyzed. The energy difference between the axial and the equatorial form is Δ G ° = 0.8 ± 0.4 kcal/mole and Δ E 0,0 = 0.54 ± 0.15 kcal/mole in C 6 H 11 Br and C 6 H 11 I, respectively, the equatorial forms being more stable. Iodine nuclear quadrupole coupling constants for equatorial and axial C 6 H 11 I have been obtained. The present analysis contributes to the microwave investigation of the cyclohexyl halides.

The high-resolution microwave spectra of the79Br and81Br isotopic species of cyclohexyl bromide, C6H11Br, have been assigned for the equatorial and axial isomers, respectively. The ground-state energy of the axial isomer is 0.72 ± 0.30 kcal/mole higher than that of the equatorial one. The quadrupole coupling constants have been obtained for the equatorial and axial ground states of both the isotopes. Several vibrational excited states of the equatorial and axial conformers (79Br) have also been analyzed.

An analysis of the microwave spectrum of HNSO and DNSO has been performed, extended with respect to a preceding work, in order to determine the first-order P 1 centrifugal distortion constants. From the b-type spectrum of DNSO, not previously assigned, the rotational constant A of this species has been evaluated. The H–N bond r s distance has been calculated to be 1.0272±0.0001 A.

The microwave spectra of 1,1′-dimethyl-2,2′-dicyanoethylene and 1,1′-dimethyl-2,2′-dicyanoethylene-d6 have been recorded in the frequency region 18–40 GHz. The measured ground state lines have been fitted to a semi-rigid rotor model. From the resulting six moments of inertia some structural information has been obtained.

Three methods are discussed to determine the electric dipole moment of asymmetric top molecules in those cases where the conventional second order Stark pattern is difficult to identify, because of spectral complexity. The methods are applied to a test molecule and to a number of molecules whose dipole moments were not previously determined.

The two isotopic species CH 2 DCOOH and CH 2 DCOOD of acetic acid have been investigated with microwave spectroscopy in order to determine the equilibrium configuration of the methyl group, which was found to be eclipsed with respect to the carbonyl group. Centrifugal distortion constants free from internal rotation effects have been determined. A r s structure for the four hydrogens and a partial r 0 structure for the whole molecule are given.

A reinvestigation of the microwave spectrum of N-methyl-p-fluoroaniline shows this molecule to have low lying excited vibrational states associated with the inversion and torsion of the HNCH3 group similar to N-methylaniline. The experimental data indicate a greater tendency towards a planar configuration at the nitrogen atom and a lower barrier to inversion compared to p-fluoroaniline.

A tunable color center laser has been used as the infrared radiation source for infrared-radio-frequency double resonance spectroscopy. The A1–A2 splitting (J, K = 1, l = 1 and J, K = 2, l = −1) in the ν4 vibrational state of CH3F has been studied. This technique has also been used to measure the electric dipole moment for the ν4 state, which has been determined to be 1.8332(23) D.

The Stark effect of rotational and torsio-rotational transitions of propargyl mercaptan has been analyzed. Assuming a dependence of the dipole moment components on the internal rotation angle of the type: μ a = μ a 0 + μ a (1) cos α , μ b = μ b 0 + μ b (1) cos α , and μ c = μ c (1) sin α , the following values of the determinable quantities were obtained: μ a eff = 0.718 ± 0.003 D , μ b eff = 0.495 ± 0.010 D , and μ c (1) = 0.809 ± 0.015 D . The SH bond moment was also evaluated from μ c (1) and compared with the SH bond moment of similar molecules.

Low resolution microwave spectra of four isotopic species and high resolution microwave spectra of two isotopic species of N-methyl-p-fluoroaniline have been recorded. The rotational constants obtained by each method were used separately for fitting the structure and the results were compared. The N-methyl-p-fluoroaniline molecule is found to be more nearly planar than aniline and p-fluoroaniline, the out-of-plane angle of the HNCH3 group being φ = 18° ± 3°.

The microwave spectrum of C4O2Cl2 (1,2-dichlorocyclobuten-3,4-dione) has been investigated for both the C4O235Cl2 and the C4O235Cl37Cl isotopomers. The spectrum of the latter has been studied in greater detail because a number of μb rotational transitions were measured with the radiofrequency-microwave double-resonance technique by radiofrequency pumping of some K−1 doublets. This pumping has been made possible since a small μa dipole moment component appears owing to the asymmetric isotopic substitution.

Application de cette methode en vue de determiner les constantes de decomposition dans l'etat (Z t ) de OsO 4

The rotational spectrum of N-methylpyrrolidine has been measured in the ground state and eight excited vibrational states. The molecule shows a bent configuration with the nitrogen atom out of the plane containing the carbon atoms and with the methyl group in the equatorial position. From the analysis of the A-E rotational splittings in the first excited state of the methyl torsion, the corresponding barrier has been calculated to be 3860 ± 50 cal/mole. The spacings between the levels of the ring puckering are in accordance with the relatively high barrier to pseudorotation previously obtained by ab initio calculations. Finally, the 14N quadrupole coupling constants and the electric dipole moment have been determined.

The ground state microwave rotational spectra of the axial and equatorial chair forms of ethynyl-cyclohexane are investigated in the frequency region 8–26.5 GHz. The spectrum of the first vibrationally excited state of the e-conformer is also assigned and intensity measurements locate this state at 130 ± 30 cm−1. Using the ground state rotational constants obtained for the two isomers, a least-squares structural analysis is performed.

The microwave spectrum of the deuterated propargyl mercaptan was recorded and measurements in the torsional levels 0± and 1± are reported. The internal rotation analysis is carried further using the new data obtained and a more specific Hamiltonian. With the mean values of the rotational constants for the two isotopic species in the states 0±, a r0-structure is proposed.

The method of radiofrequency spectroscopy inside a CO2N2O laser cavity has been applied to the observation of pure nuclear quadrupole resonance, A1-A2 transitions and two-photon transitions of AsH3. From the assignment of these transitions some coincidences between laser lines and Δk = 3 transitions in the ν2 band and Δ|k − l|; = 3 transitions in the ν4 band have been assigned. The quadrupole coupling constant eqQ and its rotational dependence χJ, χK and χd, and the spin-rotation constants CN and CK for the As nucleus have been determined for the ground state. The effective values of eqQ has been determined for the ν2 and the ν4 states.

The millimetric wave spectrum of COF 2 has been measured in the frequency range 100,000–200,000 Mc. Double resonance experiments were carried out in order to identify some previously measured low frequency lines and some of the high frequency transitions. The following values in Mc/s of the centrifugal distortion and rotational constants were obtained by centrifugal distortion analysis of all low and high frequency transitions. τ aaaa = −0·0653935 ± 0·0000921 τ bbbb = −0·0451722 ± 0·0000933 τ aabb = 0·0246729 ± 0·0008584 τ abab = −0·0351807 ± 0·0004393 A = 11813·550 B = 11753·049 C = 5880·896 The force constants corresponding to the B 1 species 2 × 2 GF matrix were also obtained. Their values are: F 44 = 4·95 ± 0·01 mdyn/A F 55 = 1·28 ± 0·02 mdynA F 45 = 0·48 ± 0·02 mdyn

The rotational “a” type spectra of H 16 O 35 Cl, H 16 O 37 Cl, D 16 O 35 Cl, D 16 O 37 Cl and D 18 O 35 Cl have been measured. The rotational constants B and C and the quadrupole coupling constants χ aa and χ bb were obtained for each isotopic species. The values of D J and D JK for H 16 O 35 Cl were also determined from centrifugal distortion analysis of the spectrum. The following values of the structural parameters were obtained: r OH = 0.959 ± 0.005 A from I a and I b , r OH = 0.975 ± 0.003 A from I b and I c , r OCl = 1.689 5 ± 0.003 5 A and

Conformational analysis of N -methyl- m -fluoroaniline has been performed by low resolution microwave spectroscopy. Two rotational isomers, corresponding in a near-planar configuration to the m -fluorine being either cis or trans with respect to the amino hydrogen, have been detected. The energy difference is found to be 270 ± 70 cal mol −1 , the cis isomer being the more stable. Ab initio calculations indicate a barrier height for the internal rotation of the HNCH 3 group around the C ph —N bond of 9.04 kcal mol −1 .

Rotational transitions in propargyl mercaptan have been assigned to the correct torsional state using the microwave double resonance technique. Details concerning the modulation of the pump oscillator are reported.

Correction et extension de l'analyse des spectres de double resonance IR-microonde et a 2 photons de AsH 3 en regard de resultats recents en IR a haute resolution

The first three direct I-type doubling transitions in the v4 = 1 state of PH3 have been measured. The I-type doubling constant q4 has been evaluated to be 5267.10(60) MHz.

The electric dipole moment of PH 3 in the v 4 = 1 state was measured by means of the Stark effect on the first two l -type doubling transitions