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 infrared spectra of the band of the 2Π–2Π asymmetric hydrogen stretching vibration in the three isotopic acetylene ions C2H2+ (ν3), 13C2H2+ (ν3), and DCCH+ (ν1) have been observed and analyzed. The high resolution infrared spectra were recorded using a difference‐frequency laser spectrometer as the tunable coherent infrared source probing an ac glow discharge. Velocity modulation, noise subtraction, and unidirectional multipassing of the infrared beam through the discharge cell provided high sensitivity. C2H2+ was produced in a gas mixture of H2, He, and either CH4 or C2H2, with a total pressure of ≊7 Torr in multiple‐inlet–outlet air‐, water‐, and liquid‐nitrogen‐cooled discharge tubes; C2H2 freezing precluded its use in liquid‐N2‐cooled discharges. Complicated by a strong perturbation whose maximum occurred at N’=15 for F1 and N’=14 for F2, the assignment of the spectrum of normal C2H2+ was made possible by (1) fortuitous discharge conditions which provided unambiguous discrimination of C2H2+ lines ...

The rotational spectra of the four monosubstituted isotopomers of protonated cyanogen HN13CCN+, HNC13CN+, H15NCCN+, and HNCC15N+, in the ground vibrational state have been investigated in the spectral region from 130–270 GHz, using a negative glow discharge production method. From the moments of inertia of the five monosubstituted species, including the DNCCN+ isotopomer [G. Cazzoli et al., Chem. Phys. Lett. 194, 297 (1992)] and of the parent species HNCCN+ [T. Amano and F. Scappini, J. Chem. Phys. 95, 2280 (1991)], the complete rs structure has been obtained. The alchemy of the ion production has been further improved compared to the previous works.

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 frequency of seven rovibrational transitions in the ν3 band, Q branch of 188OsO4 have been measured with high accuracy. The spectrometer used consists of two CO2 lasers [∼3 W on the 10R(0)], the first of which is stabilized on the 4.3 μm fluorescence Lamb dip of the CO2 and the second on the saturated absorption dip of the rovibrational transitions of 188OsO4. The OsO4 transition frequencies are obtained combining the known frequency of the first laser with the measured frequency of the beat note between the two laser beams. For the assignment of the transitions the recent Fourier transform analysis by Bobin et al. [J. Mol. Spectrosc. 122, 229 (1987)] was used. The access to the 10R(0) laser line has made it possible to investigate, for the first time, the Q branch of the ν3 band of OsO4 in a sub‐Doppler regime. Furthermore, the tetrahedral fine structure in the ground and in the ν3 state has been analyzed using the infrared–radio frequency double resonance technique. The tetrahedral splitting constan...

The highly sensitive method of radio‐frequency–infrared double resonance spectroscopy inside the cavity of a CO2 laser has been applied to the study of collision‐induced transitions of CH379Br and CH381Br in the four level scheme. Various types of radio‐frequency transitions corresponding to A1–A2 and pure quadropole resonances were observed as a result of collision population transfer between different rotational levels. Thus, collision‐induced dips have been measured in the pure gas and in mixtures with polar carbonyl sulfide (OCS) and nonpolar (He, Ar) foreign gases. Clamping experiments were also done, using a second radiation in a six level triple resonance configuration to investigate collision selection rules. The intensity ratios of the collision‐induced dips to the corresponding three level double resonance signals were measured for a number of transitions in the ground and in excited vibrational states. Collision selection rules in the pure gas and in mixtures with polar and nonpolar foreign gas...

The ground‐state rotational spectrum of protonated cyanogen, HNCCN+, has been identified following the infrared detection by Warner and Amano [J. Mol. Spectrosc. 145, 66 (1991)], using a hollow cathode discharge as production source. The rotational and centrifugal distortion constants have been determined to be 4438.010 13(71) MHz and 0.529 95(24) kHz, respectively.

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.

Electric nuclear quadrupole hyperfine structure arising from a quadrupolar nucleus at the center of tetrahedral molecules, such as 189OsO4, is symmetry forbidden. However, through vibration–rotation distortion a small nuclear quadrupole coupling is induced. The hyperfine structure due to the vibrationally induced eqQ has been measured for a number of P‐ and R‐branch transitions in the ν3 fundamental of 189OsO4, by using inverse Lamb dip spectroscopy. Microwave modulation sidebands of CO2 laser lines have been used as the tunable infrared radiation. From the analysis of the observed hyperfine structure patterns, the values of the scalar and tensor coupling constants have been determined to be χVs=−4.103±0.048 MHz and χVt=−3.090±0.059 MHz.

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 infrared spectrum of gaseous acetyl cyanide, CH3COCN, has been recorded from 90 - 3200 cm-1. The Raman spectrum of the liquid phase has been measured between 100 and 500 cm-1. The eighteen fundamental vibrations have been assigned, mainly on the basis of the infrared band contours, and a normal coordinate analysis has been made.

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 rotational spectrum of lactonitrile, CH3CH(OH)CN, has been reinvestigated. The analysis has been extended to the CH3CH(OD)CN species and to several excited states of the hydroxyl and methyl internal rotations. The molecule exhibits two conformers with the hydroxyl hydrogen gauche with respect to the cyano group. The conformer A with the hydroxyl hydrogen adjacent to the methinic hydrogen is 118±30 cm−1 (75±30 cm−1 for the OD species) more stable than the conformer B with the hydroxyl hydrogen adjacent to the methyl group. The barrier height to the interconversion is about 400 cm−1. Rotational A–E splittings due to methyl internal rotation have been observed in the first excited state of both conformers, yielding effective V3 barriers of 3.7 kcal/mol for conformer A and 4.3 kcal/mol for conformer B. By using a one‐dimensional flexible model treatment the potential function and the structural relaxation associated with the OH torsion have been determined from the level spacings and the variations of the...

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.

The microwave ground state spectrum of cis propionyl fluoride has been investigated expanding, with respect to a previous study, the range of the quantum numbers of the transitions, J up to 40 and K up to 18. At low K the spectrum resembles that of an asymmetric rigid rotor, except in a number of cases where the lines are split into A, E doublets. At intermediate and high K the mixing of the if-doublet rigid rotor wave functions makes forbidden transitions appear. The results of the analysis of the methyl top internal rotation ground state splittings are: V3 = 2350 ± 11 cal/mole, ≮ (i, a) = 32.7° ±2.0°, and Iα = 3.18 ± 0.03 uÅ2.

The analysis of the microwave spectra of some excited states of the skeletal torsion in both antiperiplanar and synclinal forms of normal propyl fluoride has been extended in order to obtain the splittings (Δ0=EE -EA ) due to the methyl group internal rotation. The results have been used, together with the experimental data already available, to obtain information on the structural relaxation upon torsional excitation and conformation exchange, and to evaluate a simple set of potential energy parameters for the two torsions by applying one- and two-dimensional flexible models.

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.

The rotational Zeeman effect of FClCO is reported. The Chlorine nuclear gI-factor, the molecular g-factors, gaa , gbb , and gcc , and the magnetic susceptibility anisotropics, (2 χaa- χbb - χcc) mole and (2 χbb - χcc - χaa) mole, are obtained from the spectrum. Some derivative molecular quantities are calculated.

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 rotation-torsion-vibration interaction in acetyl cyanide, CH3COCN, has been studied in the rotational spectra of the first excited state of the methyl torsion and of the CCN-in-plane bending. A model with two internal degrees of freedom has been used to account for the A-E rotational splittings in the ground state and in the two excited states simultaneously. The constants in the Fourier expansion of the potential hindering the methyl torsion are determined. The results are compared with those obtained in a previous work from the A-E rotational splittings of the ground state only, using a model with one degree of freedom. Group theoretical considerations are made upon the Hamiltonian used in the present analysis.

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 microwave spectra of acetyl cyanide, CH3COCN, in the ground and in the two lowest excited states have been investigated. The rotational constants and the quadrupole coupling constants have been evaluated for all these states. The internal rotation parameters have been refined with respect to previous works. Evidence for a rotation-torsion -vibration interaction has been found in the spectra of the excited states.

The ground state rotational spectrum of the trans n-propanol (CH3CH2CH2OH) has been reinvestigated expanding the frequency region, with respect to a previous study, from 8 to 40 GHz. A centrifugal distortion analysis has been carried out by measuring new transitions, including μa- transitions not observed before. The potential barrier V3 to the methyl top internal rotation has been determined from fourteen transitions which were found split into doublets. V3 is 2730 ± 60 cal/mole, ∢(i, a) = 29° ± 1°, assuming Ia = 3.193 uÅ2.

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 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

The rotational spectrum of 2-chloropyridine was measured in the region between 8-40 GHz. The rotational constants for the vibrational ground state are: A = 5872.01 ± 0.02 MHz, B = 1637.82 ± 0.02 MHz, C=1280.51 ± 0.02 MHz. The value 0.0385 amu · A2 of the inertia defect indicates a planar nuclear frame. From the hyper-fine splittings of the rotational lines the nuclear quadrupole coupling constants of 35Cl were determined. The values are: χaa = 70.79 ± 0.17 MHz, χbb = 39.01 ± 0.45 MHz, χcc = 31.78 ± 0.62 MHz.

The microwave investigation of propargyl mercaptan has been continued to study the internal rotation of the SH group in the molecule. A Hamiltonian is proposed to describe the over-all rotation and the torsion of the top. The analysis leads to the result that the potential function is a double minimum potential with a lower barrier of 470 ± 10 cm-1 at the eis position and a higher barrier of 2000 ± 500 cm-1 at the trans position.

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 derivation of some Zeeman parameters for FClCO is reconsidered and the corrected values are reported.

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

The microwave spectrum of the (CH3)2NNO and (CH3)2 15N15NO species have been studied and the rotational constants evaluated. By comparison of the inertia defects of the two species it can be stated that the nuclear frame of the molecule is planar, which is in agreement with the reported electron diffraction results. The dipole moment of the (CH3)2 15 N15NO species has been determined. Further studies on the internal rotation of the two methyl tops are in progress together with the analysis of the spectra of other isotopically substitued species.