States Of Formaldehyde Research Articles

Vibrational energy levels of the S 0 and S 1 states of formaldehyde using an accurate ab initio based global diabatic potential energy matrix

Low-lying vibrational energy levels of both the ground (S 0) and first excited singlet (S 1) states of formaldehyde have been determined using an exact kinetic energy operator and adiabatic potential energy surfaces derived from a recently developed full-dimensional global diabatic potential energy matrix (DPEM) based on a neural network representation of high level ab initio data. The agreement with available experimental band origins provides strong evidence in support of the accuracy of the DPEM, which can be used in the future for understanding the internal conversion of H2CO(S 1) and the subsequent roaming dynamics on its S 0 state.

Signatures of light-induced nonadiabaticity in the field-dressed vibronic spectrum of formaldehyde.

Nonadiabatic coupling is absent between the electronic ground X and first excited (singlet) A states of formaldehyde. As laser fields can induce conical intersections between these two electronic states, formaldehyde is particularly suitable for investigating light-induced nonadiabaticity in a polyatomic molecule. The present work reports on the spectrum induced by light-the so-called field-dressed spectrum-probed by a weak laser pulse. A full-dimensional ab initio approach in the framework of Floquet-state representation is applied. The low-energy spectrum, which without the dressing field would correspond to an infrared vibrational spectrum in the X-state, and the high-energy spectrum, which without the dressing field would correspond to the X → A spectrum, are computed and analyzed. The spectra are shown to be highly sensitive to the frequency of the dressing light allowing one to isolate different nonadiabatic phenomena.

Resummation of the Rayleigh-Schrödinger perturbation series. Vibrational energy levels of the H2S molecule.

ABSTRACT The Rayleigh – Schrödinger perturbation series possesses the property that can be termed multiple convergence. This property is that using appropriate multivalued approximants it enables the energy levels of several states to be calculated from the coefficient of a series constructed for one state. This multiple convergence property has been previously demonstrated in a number of papers: for linear anharmonic oscillators (Sergeev and Goodson J. Phys. A: Math. Gen. 31 4301 (1998)), for one-dimensional periodic problem (Fernandez and Diaz 2001, Eur. Phys. J. D15 41), for electronic sates of diatomic molecules (Jordan Int. J. Quant. Chem. Symp. 9, 325 (1975); Goodson Mol. Phys. 110, 1681 (2012)) and for vibrational states of formaldehyde (Duchko and Bykov Phys. Scr. 94, 105403, (2019)). In this paper, we examine multiple convergence as applied to the vibrational states of the hydrogen sulphide which exhibits the strong local mode behaviour. We show that property of multiple convergence is connected with the polyad structure of the vibrational energy spectrum and the strength of anharmonic resonance coupling between the states.

Neural Network Based Quasi-diabatic Representation for S0 and S1 States of Formaldehyde.

A neural network based quasi-diabatic potential energy matrix Hd that describes the photodissociation of formaldehyde involving the two lowest singlet states S0 and S1 is constructed. It has strict complete nuclear permutation inversion symmetry encoded and can reproduce high level ab initio electronic structure data, including energies, energy gradients, and derivative couplings, with excellent accuracy. It has been fully saturated in the configuration space to cover all possible reaction pathways with a trajectory-guided point sampling approach. This Hd will not only enable the accurate full-dimensional dynamic simulations of the photodissociation of formaldehyde involving S0 and S1 but also provide a crucial ingredient for incorporating spin-orbit couplings into a diabatic framework, thus ultimately enabling the study of both internal conversion and intersystem crossing in formaldehyde on the same footing.

The ν6 fundamental frequency of the à state of formaldehyde and Coriolis perturbations in the 3ν4 level.

Formaldehyde is the smallest stable organic molecule containing the carbonyl functional group and is commonly considered to be a prototype for the study of high-resolution spectroscopy of polyatomic molecules. The a-axis Coriolis interaction between the near-degenerate ν4 and ν6 (out-of-plane and in-plane wagging modes, respectively) of the ground electronic state has received extensive attention and is thoroughly understood. In the first excited singlet à (1)A2 electronic state, the analogous Coriolis interaction does not occur, because the à state suffers from a pseudo-Jahn-Teller distortion, which causes a double-well potential energy structure in the q4 (') out-of-plane coordinate, and which dramatically reduces the effective ν4 (') frequency. The ν4 (') frequency is reduced by such a great extent in the à state that it is the 3ν4 (') overtone which is near degenerate with ν6 ('). In the current work, we report the precise ν6 (') fundamental frequency in the à state, and we determine the strength of the a-axis Coriolis interaction between 3ν4 (') and ν6 ('). We also provide a rotational analysis of the ν4 (')+ν6 (') combination band, which interacts with 3ν4 (') via an additional c-axis Coriolis perturbation, and which allows us to provide a complete deperturbed fit to the 3ν4 (') rotational structure. Knowledge of the Coriolis interaction strengths among the lowest-lying levels in the à state will aid the interpretation of the spectroscopy and dynamics of many higher-lying band structures, which are perturbed by analogous interactions.

Rotationally resolved doubly-resonant three-photon ionization investigation of the 3px ¹A₂ Rydberg state of formaldehyde

Rotationally resolved doubly-resonant three-photon ionization investigation of the 3px ¹A₂ Rydberg state of formaldehyde

A theoretical study on the spectroscopy and the radiative and non-radiative relaxation rate constants of the S01A1–S11A2 vibronic transitions of formaldehyde

We have carried out a close examination on the mathematical treatments and the first-principle computations concerning the vibronic transitions between the S(0)(1)A(1) and the S(1)(1)A(2) states of formaldehyde. The simulation of absorption spectrum was presented with peak intensities calculated according to vibronic-coupled transition dipole moments and Franck-Condon factors. The radiative and non-radiative transition rate constants from the excited to the ground states were calculated with formulas based on Fermi's golden rule. It is concluded that our simulated absorption spectrum between 300 and 360 nm, as well as the estimated relaxation rate constants, showed good agreements with experimental reports.

Rotational transitions within the 21, 31, 41, and 61 states of formaldehyde H212C16O This article is part of a Special Issue on Spectroscopy at the University of New Brunswick in honour of Colan Linton and Ron Lees.

This work, besides its fundamental interest, is motivated by the atmospheric and astrophysical importance of formaldehyde (H2CO). The goal of this study is to complete the already existing list of rotational transitions within the ground vibration state by a list of transitions within the four first excited 21, 31, 41, and 61 vibrational states, to help the detection of this species by microwave or millimetre wave techniques. For this purpose, the rotational spectra of H2CO in the 21, 31, 41, and 61 excited vibrational states have been investigated in Lille and Cologne in the millimetre region at 160–600 GHz and 850–903 GHz, respectively. The results of these millimetre wave measurements were combined with the 21, 31, 41, and 61 infrared energy levels, which were obtained from previous analysis of FTS spectra of the ν4 (out of plane bending mode), ν6 (CH2 rock mode), and ν3 (CH2 bending mode) bands recorded in the 10 µm region (D.C. Reuter, S. Nadler, S.J. Daunt, and J.W.C. Johns. J. Chem. Phys. 91, 646 (1989)) and more recently for the ν2 fundamental band (C=O stretching, located at 1746.009 cm–1) (F. Kwabia Tchana, A. Perrin, and N. Lacome. J. Mol. Spectrosc. 245, 141, (2007)). The energy level calculation of the 21, 31, 41, and 61 interacting states accounts for the various Coriolis-type resonances that perturb the energy levels of the 21, 31, 41, and 61 vibrational states as well as for the anharmonic resonances coupling the 21 and 31 energy levels, and in this way the microwave and infrared data could be reproduced within their associated experimental uncertainty. However, it is clear that the theoretical model used to account for the very large A-type Coriolis resonance linking the 41 and 61 energy levels of H2CO is only effective with poor physical meaning.

Solvent effects in electronically excited states using the continuum solvation model COSMO in combination with multireference configuration interaction with singles and doubles (MR-CISD)

An implementation of the COSMO continuum solvation model into the MCSCF and MR-CISD programs of the COLUMBUS program system is reported. Equilibrium solvation and non-equilibrium solvation models for the treatment of electronic excitations have been used. Solvatochromic effects have been computed for a representative set of n-π* and π-π* states of formaldehyde, acrolein and pyrazine using several solvents ranging from some with apolar character to water. Agreement with experimental shifts is good within the limits of a continuum model.

Rotational structure in the Ã1A″–X̃1A′ spectrum of formyl chloride

High-resolution cavity ring-down spectroscopy has been used to record three vibronic bands of the A1A″–1A′ (π*â†�nO) transition of room-temperature formyl chloride (HClCO). These three bands (601, 501601 and 201501601) are all vibronically induced through the activity of the out-of-plane inversion vibration ν6, and are found to obey type-a selection rules. Rotational constants have been derived from the analysis of these bands and used to give information on the geometrical structure of the excited state. The properties of the Astate are found to be intermediate between those of the corresponding states of formaldehyde and formyl fluoride.

Urea-Formaldehyde Resins and Free Formaldehyde Content

Specifications of wood adhesives must be in correlation with the requirements for the corresponding wood products, for which they will be used. Formaldehyde emission of wood products bonded with urea-formaldehyde resin based adhesives is strictly regulated by standards and there is a compromise is between formaldehyde emission and performance, such as strength, or water resistance. Since values of formaldehyde emission depend on the test method used, in Europe urea-formaldehyde resins for adhesives may generally be classified according to HCHO emission in the particleboard rating of Emission 0 to Emission I class (E-0 to E-1). According to DIN EN 120, particleboard quality E1 emits <6.5 mg/100 g dry article determined with the perforator method. Although a great number of factors effect the formaldehyde emission of the cured products, such as the hardener system, the type of wood etc., the emission of formaldehyde is in strict correlation with the free formaldehyde content of the resin before the curing process. E1 emission class can be achieved, if the free formaldehyde content of the resin is lower than 0.2% by mass. Urea-formaldehyde resins containing. higher than 0.5% free formaldehyde by mass exceed emission class E2, and are not accepted. Since the free formaldehyde content of the urea-formaldehyde resin effects the emission of formaldehyde in the cured product, low formaldehyde content must be ensured during resin synthesis. This can be achieved by properly selecting synthesis conditions as well as raw materials. The quality of raw materials is an essential and determining factor for the synthesis of urea formaldehyde resins. The principal changes which may take place in the formaldehyde solution on storage are the polymerization and precipitation of the polymer, Cannizzaro reaction, methylal formation, oxydation to formic acid, condensation to hydroxyaldehydes and sugars. Any of these reactions are detrimental to product quality. The state of formaldehyde is also an essential factor, since the reaction of poly(methylene glycol)s with urea leads to methylene ether linkages resulting in emission of formaldehyde during storage and later on during the process of curing. Hydrolysis, isomerisation and decomposition of urea may take place simultaneously during improper storage conditions, such as high humidity, high temperatures, industrial atmosphere. The side products formed affect the reaction with formaldehyde during the synthesis resulting in high free formaldehyde content of urea-formaldehyde resins. The relation between synthesis conditions, free formaldehyde content and performance of urea-formaldehyde resins are discussed in detail.

A time-dependent approach to the nonradiative decay of polyatomic molecule: S 1 to S 0 transition of H 2CO

A time-dependent method to estimate a nonradiative transition rate was proposed and applied to the problem of decay of S 1 to S 0 state of formaldehyde. This approach is based upon the wave packet propagation with the reaction path Hamiltonian and the direct calculations of electronic matrix elements of nonadiabatic coupling using ab initio MO method. Since the auto-correlation function, operated with a Fourier transformation to obtain the rate constant, decays within a short time by introducing the effective Hamiltonian in time propagator, it is possible to estimate the rate constant by short time propagation of wave packet. The calculated nonradiative decay rates were in good agreement with the experimental ones.

Low-energy electron-impact excitation of the 3,1A2(n--> pi *) states of formaldehyde.

A three-state calculation of electron-impact excitation of formaldehyde to the a^3A_2 and A^1A_2 states is carried out using the Schwinger multichannel variational method. The integral and differential cross sections so obtained agree fairly well with theoretical results obtained using the complex Kohn method. Though agreement between the calculated integral cross section and the single available experimental measurement is qualitative, similar conclusions regarding the excitation mechanism are reached. A generalization of the selection rule for (Σ^+⇆Σ^−) electron-impact excitation of diatomic molecules is used to explain the shape of the differential cross sections for the a^3A_2 and A^1A_2 excitations.

Analytic energy gradients for open-shell coupled-cluster singles and doubles (CCSD) calculations using restricted open-shell Hartree—Fock (ROHF) reference functions

The theory of analytic energy gradients for the open-shell single and double excitation coupled-cluster (CCSD) method based on restricted open-shell Hartree—Fock (ROHF) reference functions is presented. The new CCSD gradient method is applied to the dissociation of the 3A″ state of formaldehyde (CH 2O) to H and HCO. Complete geometry optimization is carried out for the initial reactant, the transition state of the reaction, and for the dissociation products. Non-iterative triples appropriate to ROHF are introduced and are used to define a new ROHF-CCSD(T) method. Using this approach and zero-point corrections, the activation energy is calculated to be 21.0 kcal/mol and the exit barrier height is predicted to be 6.1 kcal/mol, both in excellent agreement with experiment.

Variational study of the excited vibrational states of formaldehyde: accurate results up to 8500 cm^−1 in excitation energy

Variational results of the vibrational states up to 8500 cm−1 for X1A1 formaldehyde at J = 0 are presented. Our results agree reasonably well with perturbation results and with experimental results. Our calculations show additional b1 and b2 states in the energy region of the 2244 level, which could not be predicted by a simple normal-mode analysis. We also found that the eigenstates in this energy regime, seen from the zero-order normal-mode picture, have variety of characters: some states appear much more mixed than others.

High precision dipole moments in à 1A2 formaldehyde determined via Stark quantum beat spectroscopy

The high resolution technique of Stark quantum beat spectroscopy is used to examine the electric dipole moment function for the first excited singlet state (à 1A2) of formaldehyde-h2 and formaldehyde-d2. The high precision of these measurements (i.e., better than 5 parts in 104) enables detailed determination of a-axis dipole moment components (μa ) for individual J=2 rovibronic levels in the ν4 out-of-plane bending mode. In the case of 21,1 rotational levels, we find μa (40)=1.4784(7) D and μa (41)=1.4678(4) D for H2CO. For D2CO the measured 21,1 dipole moments are μa (40)=1.4698(6) D, μa (41)=1.4693(3) D, and μa (43) =1.4786(7) D. The state-specific variations in μa revealed by this study reflect the structural influences exerted by the pervasive S1∼S0 nonadiabatic interactions and the pyramidally distorted equilibrium configuration which characterize the à state of formaldehyde. The origin and experimental manifestation of the out-of-plane dipole moment component (μc ) in nonrigid à 1A2 formaldehyde is also discussed.

Self-consistent group calculations on a simple model for the photochemical ? cleavage reaction of carbonyl compounds

Potential energy surfaces were calculated for the ground and some excited states of formaldehyde as a model for the α cleavage reaction of carbonyl compounds. Computations were based on an STO-3G basis within the SCGF approach. Only planar geometries were considered. The VB-CI description of the group of electrons directly involved in the reaction allows for a general and illuminating discussion of the wave functions for this reaction and gives a theoretical justification of the configuration mixing model of Pross [8].

Double-well potential surface and associated vibrational frequencies in the ā 3A 2 nπ * state of formaldehyde

A double-well potential surface has been computed for the out-of-plane bending and the CO stretching vibrations of the lowest ā 3A 2 excited electronic state of H 2CO. The vibrational levels of the coupled oscillators have been calculated using a variational treatment. The barrier height of inversion as well as the symmetric (+)-antisymmetric (−) splittings and the vibrational energies are reported.

Barrier height to inversion of aliphatic carbonyl compounds in the S1(n,π*) state; ab initio study of formaldehyde

Abstract Recently the double-minimum potentials for the pyramidal distortion in the S 1 (n,π*) state of a number of aliphatic carbonyl compounds like acetaldehyde, acetone and cyclic ketones have been determined using the supersonic nozzle beam technique We have found a good correlation between the barrier height to inversion and the angle between the two bonds adjacent to the carbonyl carbon atom. In order to elucidate the correlation in more detail, we performed ab initio calculations for the S 1 state of formaldehyde with the HCH angle as a parameter. The SCFCI calculation verified the observed correlation. It is postulated that the barrier height can be correlated with a single geometric parameter, the HCH angle.

Ab initio study of the X, ã, Ã and B states of formaldehyde

The optimum geometrical structures of formaldehyde in the ground state (X1A1), the (n, π*) states (a3A″ and A1A″), and the lowest Rydberg state (3s, B1B2) have been obtained using SCF and GVB energies and a few basis sets built on the usual double zeta (DZ) set. In the quasi-Newton optimization process an approximate force constant (Hessian) matrix is obtained for no extra cost and, by comparison with other methods, it is shown that the approximate Hessian yields reasonable vibrational wavenumbers in most cases. The out-of-plane bending potential is studied in the a and A states, and the excitation energies from the ground state to the a, A and B states are compared with experimental values.