The rotation-vibration spectrum and double-minimum ν12 potential function of propadienone: A semirigid bender analysis

Propadienone is an interconverting molecule having a pair of equivalent symmetry related conformers separated by an energy barrier rising well above the vibrational ground state. Microwave spectra of molecules in excited states of the large-amplitude in-plane bending mode ν₁₂, including intersystem lines, have been successfully represented using the semirigid bender model. The model reveals a double-minimum bending potential with a barrier rising 359 cm⁻¹ above the minima at C₁C₂C₃ = 142°. In the ground state the interconversion frequency is 3.7 GHz and the ν₁₂ fundamental frequency is predicted to be 160 cm⁻¹. Analysis of other vibrational satellites involving the lowest-frequency out-of-plane mode ν₈ indicates a vibrational frequency of 240 cm⁻¹. The inplane vibrational satellite and also the ground state substitution spectra are quite accurately reproduced by the model. Our generalized semirigid bender method offers a variety of approaches to fitting molecular parameters to the experimental data.     

HCNO as a semirigid bender: The degenerate ν4 state

The semirigid bender Hamiltonian for fulminic acid HCNO (Bunker, Landsberg, and Winnewisser, J. Mol. Spectrosc.74, 9–25 (1979)) is extended. The extended Hamiltonian describes the manifold of large amplitude vibrational states (due to the ν₅ HCN bending mode) superimposed on a high frequency vibrational state involving excited quanta of the ν₄ CNO bending mode. Such high frequency vibrational states may be degenerate when the large amplitude coordinate is zero, and the semirigid bender Hamiltonian is modified to account for the ν₄ vibrational angular momentum around the molecular axis in the linear limit, and for l-doubling effects. The extended Hamiltonian is used to fit HCN bending and rotation energy level separations for HCNO superimposed in the ν₄ fundamental level. It is found that the effective HCN bending potential in the ν₄ state is very similar to that in the high frequency vibrational ground state. The results obtained confirm the conclusion reached by Bunker, Landsberg, and Winnewisser: HCNO is linear at equilibrium.     

Simultaneous Analysis of Rovibrational and Rotational Spectra of thev5= 1 andv8= 1 Vibrational Levels of Propyne

The microwave and submillimeter wave spectra of propyne between 17 and 358 GHz were measured and the rotational transitions in thev₈= 1 excited vibrational state of the CH₃rocking vibration were assigned. About 1050 wavenumbers of the ν₈vibration–rotation fundamental band and about 600 wavenumbers of the ν₅fundamental band of the[formula]stretching vibration were assigned from the infrared spectrum between 910 and 1130 cm⁻¹which was used previously (G. Graneret al., J. Mol. Spectrosc.161,80–101 (1993)) in the analysis of the combinationv₉=v₁₀= 1 and thev₁₀= 3 overtone levels (ν₉being the[formula]bending and ν₁₀the[formula]bending vibrations). The rovibrational and rotational data corresponding to the two fundamental levels were analyzed simultaneously in least-squares fits using a model which treats together all the vibrational levels in the region around 1000 cm⁻¹with their strong anharmonic and vibration–rotation resonances. The refined parameters reproduce the infrared and submillimeter wave data of thev₅= 1 level with standard deviations of 0.32 × 10⁻³cm⁻¹and 59 kHz, respectively, while for thev₈= 1 level the standard deviations were 0.41 × 10⁻³cm and 290 kHz. The refined parameters of the combination and overtone levels provide reliable predictions for future submillimeter wave studies.     

The infrared spectrum of carbon suboxide in the ν6 fundamental region: Experimental observation and semirigid bender analysis

The infrared spectrum of carbon suboxide, C₃O₂, was measured at high resolution in the region from 500 to 600 cm⁻¹. The spectrum was recorded with a Bomem interferometer at a resolution of about 0.004 cm⁻¹; after deconvolution a resolution of about 0.002 cm⁻¹ was attained. Seven bands were identified and assigned to rovibrational transitions of ¹²C₃¹⁶O₂. These consist of the ν₆ fundamental band and some of the hot bands associated with the ν₇, 2ν₇, and 3ν₇ states. The data obtained on the ν₆ + nν₇ states were used as input for a semirigid bender fit yielding the effective CCC bending potential energy function in the ν₆ state together with a number of related parameters. From the results of the present work together with the results of previous semirigid bender fits it was found that C₃O₂ is bent at equilibrium with an equilibrium CCC bond angle of 156° and a barrier to linearity of 28 cm⁻¹.     

HCNO as a semirigid bender

The semirigid bender Hamiltonian [Bunker and Landsberg, J. Mol. Spectrosc., 67, 374–385 (1977)] is used to fit the rotation-vibration energy level separations in the fulminic acid (HCNO) molecule. The allowance made in the model for the variation of the CH and CN bond lengths with the HCN bending angle proves to be very important, and as well as achieving a good fit we are able to make a detailed investigation of the shape of the HCN bending potential function.From the results we conclude that the equilibrium structure of HCNO is linear but that excitation of the ν₁ or ν₂ stretching vibrations gives rise to an effective HCN bending potential function having its minimum at a nonlinear configuration. Even in the ground state the zeropoint vibrational contributions from ν₁ and ν₂ to the effective HCN bending potential give a small barrier (11.5 cm^?1) to linearity, and we determine that the zero-point HCN bending vibrational amplitude is ±34°.     

Accurate rotational spectroscopy of sulfur dioxide, SO2, in its ground vibrational and first excited bending states, v2 = 0, 1, up to 2 THz

Approximately 150 pure rotational transitions each have been recorded for SO₂, v₂ = 0 and 1, in selected frequency regions up to 2 THz. The J and K_a quantum numbers reach very high values: 92 and 23, respectively, for the ground vibrational state and 81 and 21, respectively, for the first excited bending state. The highest levels accessed are almost 3000 cm⁻¹ above ground. The relative experimental uncertainties Δν/ν are about 10⁻⁸ for several medium to strong, isolated lines, and generally better than 2.5 × 10⁻⁷. Improved spectroscopic parameters have been obtained for both states, particularly for the excited bending state. In fact, the accuracies with which the energy levels of the v₂ = 1 state are known depend essentially only on the accuracy with which the vibrational spacing is known from infrared spectroscopy.     

C3O2 as a semirigid bender: The degenerate ν5 state

The semirigid bender Hamiltonian for carbon su?ide C₃O₂ [P. R. Bunker, J. Mol. Spectrosc.80, 422–437 (1980)] is extended in a manner similar to the extension previously described for HCNO [P. Jensen, J. Mol. Spectrosc.101, 422–439 (1983)]. The extended Hamiltonian describes the manifold of large-amplitude vibrational states (due to the ν₇ CCC bending mode) superimposed on a high-frequency vibrational state involving excited quanta of the CCO bending modes ν₅ and ν₆. The extended model is used to fit CCC bending and rotation energy level separations for¹²C₃¹⁶O₂ superimposed on the ν₅ fundamental level. Due to the severely limited experimental data it is not possible to unambiguously determine the effective CCC bending potential energy function in the ν₅ state, but estimates of the potential energy parameters are obtained by determining them in two limiting cases.     

Vibrational modes of the stibine molecule

In this paper, we use the algebraic approach to describe the vibrational modes of stibine molecule (of C_3v molecular symmetry group) up to 21 quanta. As the stibine molecule exhibits stretch-bend resonances, we build an algebraic pyramidal coupling operator between stretching modes and bending modes adapted to this molecule. The standard deviation associated to the fit of the vibrational levels is 1.75 cm⁻¹.     

Diode laser spectroscopy of several bands of hydroxylamine

Diode laser spectroscopy has been carried out on the ν₅ (1115 cm⁻¹) and ν₆ (895 cm⁻¹) fundamentals, the 2ν₉ overtone, the 3ν₉-ν₉ hot band, and the ν₅-ν₉ difference band (all near 700 cm⁻¹) of hydroxylamine (NH₂OH). (ν₅ = NH₂ wag, ν₆ = NO stretch, and ν₉ = OH torsion.) Transition frequencies were determined with a nominal accuracy of ±0.001 cm⁻¹. Accurate molecular parameters were determined for the ground state, v₆ = 1, v₉ = 1, and v₉ = 2. The v₅ = 1 and v₉ = 3 states were perturbed by a Coriolis interaction with each other and possibly with a third state. In these cases effective rotational and distortion constants were determined together with empirical perturbation parameters. The data obtained on ν₅ and ν₆ enabled assignments of the transitions involved in the optically pumped hydroxylamine FIR laser to be made.     

Millimeter-wave spectrum of the C4v molecule IOF5: l-type doubling of the kl = −1 transitions in the v11(E) = 1 state spectrum

Measurements of the rotational spectrum of the C_4v molecule IOF₅ are reported for the excited vibrational state v₁₁(E) = 1 for the transitions J13 ← 12, 14 ← 13, 16 ← 15, and 17 ← 16 (55–72 GHz) including the observation of the kl = −1 (q⁻), l-doubling effect. Detailed assignments of the E-state spectrum are presented based on the overlapping quadrupole structure. These data are analyzed together with earlier results for the excited vibrational state v₆(B₁) = 1 to give information concerning the ν₆(B₁)-ν₁₁(E) Coriolis interaction and the (Δl, Δk) = (2, 2) (q⁺) and (2, −2) (q⁻)l-resonance interactions. It is found that q₁₁⁻ = −2.57(10) MHz, |q₁₁⁺| = 0.094(20) MHz, Δ = ν₆ − ν₁₁ = 45.2(7) cm⁻, ζ_11,11^z = +0.18(1) and |ζ_6,11^y| = 0.73(4).     

The rotational spectrum of acrylonitrile in excited states of the two low-frequency CCN bending vibrational modes

The strongest vibrational satellites in the rotational spectrum of acrylonitrile have been assigned and frequencies of μ_a- and μ_b-type transitions in the frequency range 27–184 GHz are reported for the first two excited states in the lowest frequency in-plane CCN bending vibrational mode and the first excited state in the out-of-plane CCN bending mode. The values of the rotational constants, the quartic and sextic centrifugal distortion constants, and one octic centrifugal distortion constant are determined for each of these states. Less extensive results are also presented for the third quantum of the in-plane bend. The data set for the ground state has been extended by a number of new measurements and the improved ground state constants are used in a discussion of changes in rotational and centrifugal distortion constants with vibrational state where all constants associated with P_zⁿ and P²P_z⁽ⁿ⁻²⁾ terms in the Hamiltonian are found to reflect the common origin of the two CCN bends.     

Mesure de la diffusivité longitudinale de matériaux anisotropes

Measurement of in-plane diffusivity of anisotropic solid samples. Survey of the techniques developed at LEMTA. Three techniques for the measurement of in-plane diffusivity of anisotropic solid samples have been developed at the Laboratory and are presented here :

• •the two directional heat pulse (flash) method with local contact measurement of two temperatures;
• •the fin method with local contact or contactless measurement of two temperatures;
• •the two directional heat pulse method with measurement of the temperature field by an infrared camera and data processing through integral transformations.

     

Study of the ν3 and 2ν3 ← ν3 bands of 12CH3F by infrared laser sideband and submillimeter-wave spectroscopy

An infrared laser sideband spectrometer operating in the CO₂ laser region with 8- to 18-GHz sidebands has been used to record 266 transitions in the ν₃ band and 84 transitions in the 2ν₃ ← ν₃ band of ¹²CH₃F. The accuracy of the measured frequencies is estimated to be 1–3 MHz. A millimeter/submillimeter-wave spectrometer has been used to record the spectra of 48 pure rotational transitions in the ground vibrational state and 55 transitions in the v₃ = 1 vibrational state with an accuracy of 20–90 kHz. The new measurements have been combined with previous radio frequency and infrared laser results to derive sets of constants for the ground, v₃ = 1, and v₃ = 2 states for this molecule. Tables of the vibrational dependence of the parameters and of the near coincidences of the ν₃ and 2ν₃ ← ν₃ band transitions with CO₂ laser frequencies are given.     

A refined potential energy function for the electronic ground state of H2Se

The potential energy surface for the electronic ground state of the hydrogen selenide molecule has been determined previously by Jensen and Kozin [J. Mol. Spectrosc. 160 (1993) 39] in a fitting to experimental data by means of the MORBID computer program. We report here a further refinement of this surface, also made with the MORBID program. With the refined potential surface, we can make predictions of rotation-vibration transition wavenumbers for H₂Se, D₂Se, and HDSe, and with these predictions we can assign weak spectra of these molecules. We assign here two very weak bands of HD⁸⁰Se, ν₁+ν₂+ν₃ and 2ν₁+ν₃. The refinement of the potential energy surface was made possible because (1) the number of vibrational states characterized experimentally for various isotopomers of H₂Se has approximately doubled since 1993, and (2) we now have access to larger computers with which we can fit energy spacings of states with J?8, whereas Jensen and Kozin could only use J?5. In the present work, we fitted rotation-vibration energy spacings associated with 24 vibrational states of H₂⁸⁰Se with v₁?6, v₂?3, and v₃?2; 11 vibrational states of D₂⁸⁰Se with v₁?2, v₂?3, and v₃?2, and 17 vibrational states of HD⁸⁰Se with v₁?3, v₂?3, and v₃?3. The input data set comprised 3611 energy spacings. In the fitting, we could usefully vary 29 potential energy parameters. The standard deviation of the fitting was 0.12 cm⁻¹ and the root-mean-square deviation for 49 vibrational term values was 0.59 cm⁻¹.     

The a-type rotational spectrum of isocyanic acid,HNCO, in the excited bending states

Rotational transitions of HNCO in the v₄ = 1, v₅ = 1, and v₆ = 1 vibrational states have been measured. The assignment of the a-type ^qR_K and ^qQ₁ branches has been made with the help of a qualitative discussion of the vibration-rotation interactions. Effective rotational and centrifugal distortion constants have been determined precisely for each vibrational K_a-rotational state, up to K_a = 4 for the lowest excited state and K_a = 3 for the other two excited states. The K_a dependence of the effective rotational constants B and D was observed to be quite anomalous for some of the transitions because of the a-type Coriolis interactions and accidental b-type Coriolis resonances. From a discussion of the selection rules and the effect on B and D of the interactions, the first excited state of the out-of-plane vibration, ν₆, has been assigned definitely to the second lowest excited vibrational state of HNCO.     

The a-type rotational spectrum of HNCS in the excited bending states

The microwave and millimeter wave spectra of HNCS in the three bending excited states, v₄ = 1, v₅ = 1, and v₆ = 1, have been measured. The ^qR₀, ^qR₁, and ^qR₂ branches for each of these three states and the ^qR₃ branch for the lowest excited state have been assigned. Effective rotational and centrifugal distortion constants have been determined for each vibrational and K_a-rotational sub-state. Two local resonances, caused by the Coriolis induced asymmetry interaction and a b-type Coriolis resonance, allow unambiguous confirmation of the assignment of the state v₆ = 1, the first excited state of the out-of-plane vibration.     

The ν2 infrared band of 1-phosphapropyne CH3CP

The Fourier transform infrared spectrum of 1-phosphapropyne CH₃CP has been recorded in the region 1470–1580 cm⁻¹ with a resolution of 0.01 cm⁻¹, and the ν₂ band centered at 1558.7416(28) cm⁻¹ was analyzed. The 689 observed transitions with J′ and K′ values up to 69 and 8, respectively, were assigned. A set of the spectroscopic constants determined for the upper v₂ = 1 state reproduced the experimental wavenumbers with an rms error of 0.0025 cm⁻¹. No significant perturbations were observed. The ν₂ + ν₈ − ν₈ hot band, centered at 1553.5492(35) cm⁻¹, was also analyzed. The upper state constants determined from the 341 observed transitions with J′ and K′ values up to 53 and 6, respectively, reproduced the experimental wavenumbers with an rms error of 0.0047 cm⁻¹.     

Low frequency vibrations of 1,3-butadiene, 1,3-butadiene-d4, and 1,3-butadiene-d6

The absorption bands in the far infrared due to the torsional and in-plane skeletal bending vibrations have been examined in detail together with some mid-infrared bands. Torsional energy level spacings up to v₁₃ = 5 for butadiene and up to v₁₃ = 4 and 3, respectively, for the d₄- and d₆-compounds have been measured accurately, and the data used to investigate the nature of the potential function for rotation about the CC single bond. A Coriolis interaction between the torsion and the in-plane bending mode ν₂₄ has been analyzed in detail.     

Observation of the v = 1 ← 0 band of SH (X2Π) with a difference frequency laser

The fundamental vibration-rotation band of SH (X²Π) has been studied in absorption at Doppler-limited resolution with an estimated accuracy of 0.002 cm^?1. The band origin (ν₀ = 2598.7675 ± 0.0003 cm^?1) and the molecular constants for the excited vibrational state (v = 1), as well as improved molecular constants for the ground vibrational state, have been determined in a least-squares fit.