Watson Hamiltonian Research Articles

Quantum dynamics study on multichannel dissociation and isomerization reactions of formaldehyde

We study quantum dynamics of the multichannel reactions of H(2)CO including the molecular and radical dissociation channels as well as the isomerization ones, H(2)CO-->trans-HCOH and trans-HCOH-->cis-HCOH. For this purpose, the previously developed potential energy function [T. Yonehara and S. Kato, J. Chem. Phys. 117, 11131 (2002)] is refined to give accurate transition state energies and to describe the radical dissociation channel. The cumulative reaction probabilities for the molecular dissociation and two isomerization channels are calculated by using the full Watson Hamiltonian. We also carry out wave packet dynamics calculations starting from the transition state region for the molecular dissociation. A contracted basis set for the angular coordinates is constructed to reduce the size of dynamics calculations. The intramolecular vibrational relaxation dynamics is found to be fast and almost complete within 300 fs. Using the energy filtered wave functions, the time propagation of HCOH population is obtained in the energy range from 81 to 94 kcal/mol. The branching ratio of the radical product is estimated by calculating the time dependent reactive fluxes to the molecular and radical dissociation products.

Vibrational behavior of tetrahedral d 0 oxo-compounds: A theoretical study

The vibrational behavior of a series of tetrahedral d 0 oxo-compounds of general formula MO 4 n - , namely CrO 4 2 - , MnO 4 - , MoO 4 2 - , RuO 4, WO 4 2 - , ReO 4 - and OsO 4, was investigated by the means of density functional theory. Both harmonic and anharmonic spectra of such systems were computed, in the gas phase, using a variational treatment to solve the vibrational Schrödinger equation considering the rotationless Watson Hamiltonian and including up to anharmonic quartic force fields terms. The effect of basis functions, both for the oxygen and metal atoms, as well as the effect of the pseudo potential used in the description of the metal were discussed in the attempt to propose a easy to handle and cost effective computational approach to compute the vibrational properties of simple d 0 compounds.

High-resolution infrared spectroscopy and ab initio studies of the cyclopropane-carbon dioxide interaction

A jet-cooled high-resolution infrared spectrum of the cyclopropane-carbon dioxide complex was detected for the first time, using a rapid scan infrared spectrometer with an astigmatic multipass sample cell. The spectrum was recorded in the vicinity of the CO2 asymmetric stretching band (nu3) and exhibits a b-dipole selection rule. Altogether, over 200 lines were observed, assigned, and fitted to Watson's S-reduction Hamiltonian. Rotational and quartic distortion constants were obtained. The band origin was located at 2347.6263(2) cm(-1), redshifted by 1.5230(2) cm(-1) from the corresponding frequency of the CO2 monomer. The experimentally determined structure shows that CO2 lies next to a C-C bond edge and is perpendicular to the C3 ring, indicating that the interaction is characterized by the bonding between the carbon atom of CO2 and the pseudo-pi system of cyclopropane. The intermolecular distance between the carbon atom of CO2 and the center of mass of cyclopropane was determined to be 3.667(2) A. Complete ab initio geometry optimizations and harmonic frequency calculations were carried out at the level of second-order Moller-Plesset perturbation theory with four different basis sets: cc-pVDZ, 6-311++G(d,p), aug-cc-pVDZ, and aug-cc-pVTZ. The lowest-energy structure identified with the three larger basis sets is in accord with the experimental finding. In addition, a transition state was identified and the tunneling barrier height was computed.

High resolution FTIR spectroscopy on CH2DI and CHD2I: analyses of the fundamental bands ν6' and ν6''

The H–C–I and D–C–I deformations, i.e. ν6' and ν6″ fundamental vibration bands of the methyl iodide molecules CH2DI and CHD2I have been investigated with high resolution (0.001 cm−1) Fourier transform infrared spectra in the region 600–1000 cm−1 for CH2DI and 550–850 cm−1 for CHD2I. For CH2DI ν6′ appears as a hybrid a/b-type band and ν6″ as a c-type band. For CHD2I the corresponding types are hybrid a/c and b. We have been able to assign more than 12 000 transitions in the case of CH2DI and over 11 000 transitions in the case of CHD2I. The upper and ground state parameters have been obtained by fitting these transitions to the A reduced Watson's Hamiltonian. The interactions between the states v6′=1 and v6″=1 have also been investigated.

A High-Resolution FT-IR Study of the Fundamental Bands ν7, ν8, and ν18 of Ethene Secondary Ozonide

Ozonization reaction of ethene in neat film at 77 K was performed. Separation of ethene secondary ozonide from the other products of the reaction was performed by continuous pumping of the reactor. Only the products, which evaporated from the walls of the reactor at 185 K, were transferred to the gas cell. The high-resolution infrared absorption spectrum of gaseous ethene secondary ozonide (C(2)H(4)O(3)) in a static gas long-path absorption cell has been recorded in the 900-1100 cm(-1) spectral region at 185 K. The spectral resolution was 0.003 cm(-1). Analyses of the nu(7)(A) band at 1037.0 cm(-1), the nu(8)(A) band at 956.1 cm(-1), and the nu(18)(B) band at 1082.1 cm(-1) have been performed using the Watson Hamiltonian model (A, reduction; III(r), representation). A set of ground-state rotational and quartic centrifugal distortion constants have been obtained, and upper state spectroscopic constants have been determined for the bands investigated. A local resonance observed in nu(18) is explained as c-Coriolis interaction with nu(10) + nu(11).

High-resolution infrared analysis of seven fundamental bands of gaseous isothiazole between 750 and 1500 cm −1

The gas phase IR spectrum of isothiazole, C 3H 3NS, between 550 and 1700 cm −1 was recorded with a resolution of ca. 0.003 cm −1. The rotational structure of seven fundamental bands in the region 750–1500 cm −1 has been assigned and analysed by the Watson Hamiltonian model. A number of local resonances in the bands have been identified and explained qualitatively in terms of Coriolis interactions. For each band upper state spectroscopic constants, including band center, rotational constants, and quartic centrifugal distortion constants are given. From observed crossings due to resonances we locate the weak bands ν 9( A′) and ν 13( A′) at 1041.9(2) and 642.0(3) cm −1, respectively. The anharmonic frequencies have been determined using a cc-pVTZ basis set, at the MP2 and B3LYP levels; the two theoretical methods give very similar results for rotational constants, anharmonic band center frequencies and distortion constants, and many of these are in good agreement with experiment.

A high-resolution infrared study of five bands of 1,2,5-thiadiazole in the range 750–1250 cm −1, together with ab initio and DFT studies

The Fourier transform gas-phase IR spectrum of 1,2,5-thiadiazole, C 2H 2N 2S, has been recorded with a resolution of ca. 0.003 cm −1 in the wavenumber region 750–1250 cm −1. Five fundamental bands in this region, ν 4 ( A 1), ν 5 ( A 1), ν 11 ( B 1), ν 13 ( B 1), and ν 14 ( B 2), have been analysed by the Watson Hamiltonian model to yield ground-state rotational and quartic centrifugal distortion constants as well as upper-state spectroscopic constants. A global perturbation of the ν 4 level is explained by Fermi resonance with the 2 ν 15 level which has been located from its resonance effect. Rotational constants, harmonic and anharmonic frequencies have been calculated using a cc-pVTZ basis, at the MP2 and B3LYP methodology levels, and compared with the experimental data.

The high-resolution infrared spectrum of isoxazole vapor between 800 and 1700 cm −1

The Fourier transform gas-phase IR spectrum of isoxazole, C 3H 3NO, between 550 and 1700 cm −1 was measured with a resolution of ca. 0.003 cm −1. Ten fundamental bands in the region 800–1700 cm −1 have been analyzed by the Watson Hamiltonian model to yield upper state spectroscopic constants. A number of local resonances have been identified in the bands and explained qualitatively, and the unobserved ν 14( A″) fundamental band has been located at 897.5(5) cm −1 from its perturbation effects on the neighboring fundamentals.

Large vibrational variational calculations using ‘multimode’ and an iterative diagonalization technique

We have favoured the variational (secular equation) method for the determination of the (ro-) vibrational energy levels of polyatomic molecules. We use predominantly the Watson Hamiltonian in normal coordinates and an associated given potential in the variational code ‘Multimode’. The dominant cost is the construction and diagonalization of matrices of ever-increasing size. Here we address this problem, using pertubation theory to select dominant expansion terms within the Davidson–Liu iterative diagonalization method. Our chosen example is the twelve-mode molecule methanol, for which we have an ab initio representation of the potential which includes the internal rotational motion of the OH group relative to CH3. Our new algorithm allows us to obtain converged energy levels for matrices of dimensions in excess of 100 000.

High resolution Fourier transform infrared spectroscopy on CH2DI and CHD2I: evaluation of the ground state constants and analyses of the C-I stretching bands ν3

Abstract The high resolution (0.0010cm−1) Fourier transform infrared spectra of the partially deuterated methyl iodide molecules CH2DI and CHD21 have been recorded and analysed in the ν3 band regions around 510cm−1. The fundamental band ν3 is associated with the stretching of the C-I bond and the spectra appear therefore as an asymmetric rotor hybrid a/b-type band and hybrid a/c-type band for CH2DI and CHD2I, respectively. About 4700 transitions in the case of CH2DI and about 3900 transitions in the case of CHD2I have been assigned. The ground state rotational constants of CH2DI and CHD2I have been obtained using the ground state combination differences calculated from the assigned ν3 transitions and 16 microwave transitions from literature. The S reduced Watson's Hamiltonian has been used in the calculations. In addition, the upper state parameters describing the v3=1 vibrational states of these molecules have been determined. The obtained ground state constants as well as the upper state parameters have been compared to the corresponding constants of the symmetric top species CH3I and CD3I

The infrared spectrum of isothiazole in the range 600–1500 cm−1, including a high-resolution study of the v 11(A′) band at 818 cm−1 and the v 16(A″) band at 727 cm−1, together with ab initio studies of the full spectrum

The gas-phase high-resolution infrared spectrum of isothiazole in the range 600–1500 cm−1 has been recorded, and revised band centres obtained for a number of vibrations. An analysis of the v 11(A′) band at 818 cm−1 and the v 16(A″) band at 727 cm−1 has been performed, using the Watson Hamiltonian, A-reduction, IIIr representation. These were combined with previous microwave spectral data to provide combined analyses for rotational constants and quartic centrifugal distortion constants Δ J , Δ JK , Δ K , δ j and δ K . These extend the knowledge derived from previous microwave and IR spectral studies. The equilibrium structures and the derived harmonic frequencies were calculated by ab initio methods, using a variety of basis sets with MP2, MP4 and CCSD(T) methods, and a comparison of these with experimental data is discussed. At a pragmatic level, the closest correlation of the rotational constants with experiment is not obtained with the most sophisticated methodology. Similarly, the vibration frequencies and intensities also vary strongly with the procedure. In particular, we found that the cc-pVTZ+MP2 results probably provide the best numerical comparison with experimental IR data for this molecule.

The infrared spectrum of isoxazole in the range 600–1400 cm−l, including a high-resolution study of the v 7(A′) band at 1370.9 cm−1 and the v 16(A″) band at 764.9 cm−l, together with ab initio studies of the full spectrum

The high resolution infrared gas phase spectrum of isoxazole in the range 600–1400 cm−1 has been recorded and more precise centres obtained for a number of bands; analyses of the v 7(A′) band at 1370.9cm−1 and the v 16(A″) band at 764.9cm−1 have been performed. Use of the Watson Hamiltonian, A-reduction, IIIr-representation and simultaneous analysis of the present IR and previous microwave data, has led to rotation constants and quartic centrifugal distortion constants Δ J , Δ JK , ΔK, δ J and δ K for the ground state and for the v 16 vibrationally excited states. The equilibrium structures and the derived harmonic frequencies have been calculated by ab initio methods using triple zeta+polarization (TZVP) and cc-pVTZ basis sets, with MP2, MP4 and CCSD(T) methods. At each methodology, for closest numerical agreement between the calculated and observed rotation constants, the optimum basis set seems to be TZVP rather than cc-pVTZ basis sets. However, the order of the highest A″ and lowest A′ symmetry vibrations is only resolved by the cc-pVTZ basis set with the MP4 methodology, which does generate the experimental sequence (v 14>v 13) The CCSD(T) methodology does not lead to significant difference over either MP2 or MP4 with the TZVP basis set.

The millimeter- and submillimeter-wave spectrum of the trans–gauche conformer of diethyl ether

The results of a first investigation of the rotational spectrum of the trans–gauche conformer of diethyl ether are reported. Two spectrometers have been used to measure the spectrum in the millimeter-wave and submillimeter-wave regions and a total of 1090 absorption line frequencies in the range 108–366 GHz were obtained and analyzed. Of these lines, 902 were measured with a spectrometer employing the fast scan submillimeter spectroscopic technique (FASSST) at Ohio State and the remaining 188 were measured with the phase-lock two-loop system (PLL) in Warsaw. The spectrum was fit to within experimental accuracy with the use of the A-reduced Watson Hamiltonian. Based on relative intensity measurements, the percentage of diethyl ether at room temperature in the trans–gauche conformer was found to be 30.5(13)%, in good agreement with prior spectroscopic values and an ab initio determination based on an energy difference of 5.40 kJ mol −1 (452 cm −1) between the excited trans–gauche and ground trans–trans conformers. This work also stimulated a critical evaluation of the data acquisition and calibration procedure of the FAAAST spectrometer, the results of which will be discussed.

Calculation of converged rovibrational energies and partition function for methane using vibrational-rotational configuration interaction.

The rovibration partition function of CH4 was calculated in the temperature range of 100-1000 K using well-converged energy levels that were calculated by vibrational-rotational configuration interaction using the Watson Hamiltonian for total angular momenta J = 0-50 and the MULTIMODE computer program. The configuration state functions are products of ground-state occupied and virtual modals obtained using the vibrational self-consistent field method. The Gilbert and Jordan potential energy surface was used for the calculations. The resulting partition function was used to test the harmonic oscillator approximation and the separable-rotation approximation. The harmonic oscillator, rigid-rotator approximation is in error by a factor of 2.3 at 300 K, but we also propose a separable-rotation approximation that is accurate within 2% from 100 to 1000 K.

Cumulative reaction probabilities for the unimolecular dissociation and isomerization reactions of formaldehyde

The cumulative reaction probabilities are calculated for the dissociation and isomerization reactions of formaldehyde in the ground state by the use of the Watson Hamiltonian. We devise an efficient computational procedure for treating the vibrational angular momentum operator. We employ an improved global potential function at the CCSD(T) level derived from the MP2 level one. The resultant cumulative reaction probability for the dissociation channel is ∼1.5 times larger than that for the isomerization one at the energy region of interest. It is also found that the transition state theory reproduces the result with the full Watson Hamiltonian within 10% error.

High resolution spectroscopy of the ν3 band of the van der Waals complex Ar—DCOOH

The vibrational-rotational spectrum of the van der Waals complex Ar-DCOOH has been recorded in the spectral region of the carbonyl stretch band. This work represents the first rotationally resolved vibrational spectrum for this complex. A full set of molecular constants could be deduced by fitting 105 lines with a standard S-reduced Watson Hamiltonian. The band origin was determined to be 1725.8440(1)cm−1 which corresponds to a small red shift of 0.0309cm−1 compared to the monomer band. The rotational constants deviate only slightly from the rotational constants in the ground state, as determined by microwave spectroscopy (I. I. Ioannou and R. L. Kuczkowski, 1993, J. phys. Chem., 98, 2231).

Rotational spectrum of HCBr produced by 193-nm laser photolysis of bromoform

The pure rotational spectrum of bromomethylene (HCBr) was studied by kinetic microwave spectroscopy between 420 and 472 GHz. The HCBr radical was produced by 193-nm ArF laser photolysis of bromoform (CHBr 3). More than 130 rotational transitions for both HC 79 Br and HC 81 Br species in the ground vibrational state were measured involving 1⩽ J⩽33 and 0⩽ K a ⩽5. The spectra were well described by an S-reduced Watson Hamiltonian in the I r representation including the nuclear quadrupole and spin-rotation hyperfine terms. Rotational, centrifugal distortion, 79,81 Br nuclear quadrupole and spin-rotation coupling constants were derived for both HC 79 Br and HC 81 Br species in the ground vibrational state.

An expert system for identification of lines in vibrational-rotational spectra

An expert system for automatic identification of the complex vibrational-rotational spectra of molecules has been developed. An iteration approach is implemented in this system, in which employment of the exact combination rule is combined with determination of the spectroscopic constants by solving of the inverse problems and comparison of the calculated parameters of spectral lines with the corresponding measured values. In order to calculate the energy levels and the frequencies and intensities of lines, the Watson Hamiltonian, the Pade-Borel approximants, and generating functions are used. The system is based on the application of pattern-recognition algorithms. Recognition training makes it possible to obtain the required flexibility of the system and to use different methods of identification based on the application of combination rules both for the analysis of strong bands and for the assignment of weak single lines. The system developed can be used to analyze the spectra of the C s and C 2V molecules, as well as employ the calculated spectrum of a molecule of any type prepared in advance. This system was successfully used to identify the H 2 16 O, H 2 17 O, H 2 18 O, D2O, HDO, H 2 32 S, H 2 34 S, and H 2 33 S and molecules.

High resolution spectroscopy of the ν3 band of DCOOD

The rotation-vibration spectrum of DCOOD has been recorded in the carbonyl stretch (ν3) region. Using a standard S-reduced Watson Hamiltonian in the Ir representation, 225 lines could be fitted to a vibrational–rotational band. A full set of molecular constants was obtained. The ν3 band is found to be strongly perturbed in the Ka: 1←1 and Ka: 2←2 subband. The perturbation is attributed to a Fermi resonance with the 2ν8 overtone band and Coriolis coupling to a combination band (ν4+ν7). The band center is determined to be 1725.1218(1) cm−1 which is more than 10 cm−1 shifted compared to previous studies.

Ritz assignment and Watson fits of the high-resolution ring-puckering spectrum of oxetane

Oxetane is a four-membered ring molecule exhibiting a large-amplitude ring-puckering motion. In order to analyze this vibration we recorded a rotationally resolved far-infrared spectrum between 50 and 145 cm −1. The analysis of the ring-puckering fundamental band with the assignment of 1108 lines, has been presented in a previous paper. In the present work we present a list of further 6531 assigned transitions between the five lowest excited ring-puckering states. The 4983 term values involved in the transitions assigned in this and in the preceding work have been evaluated by the “Ritz” program, and are now available. An A-reduced Watson Hamiltonian in any of the three representations I r, II r, and III r was used to perform a fit of the assigned transitions. Precise rotational constants and quartic as well as a full set of sextic centrifugal distortion constants were obtained for the investigated ring-puckering states. For the first time, high-resolution values for the vibrational G v parameters have been obtained, and we have added terms in x 6 and x 8 to the double minimum-potential well describing the ring-puckering motion, in order to reproduce their values within the experimental accuracy. The same potential still reproduces the lower resolution values of the Q-branch origins involving higher ring-puckering states up to v rp=14 found in the previous literature.