Absorption Spectrum Of Formaldehyde Research Articles

Quantum light-induced nonadiabatic phenomena in the absorption spectrum of formaldehyde: Full- and reduced-dimensionality studies.

The coupling of a molecule to a cavity can induce conical intersections of the arising polaritonic potential energy surfaces. Such intersections give rise to the strongest possible nonadiabatic effects. By choosing an example that does not possess nonadiabatic effects in the absence of the cavity, we can study, for the first time, the emergence of these effects in a polyatomic molecule due to its coupling with the cavity taking into account all vibrational degrees of freedom. The results are compared with those of reduced-dimensionality models, and the shortcomings and merits of the latter are analyzed.

Time-Resolved Broadband Cavity-Enhanced Absorption Spectroscopy behind Shock Waves.

A fast and sensitive broadband absorption technique for measurements of high-temperature chemical kinetics and spectroscopy has been developed by applying broadband cavity-enhanced absorption spectroscopy (BBCEAS) in a shock tube. The developed method has effective absorption path lengths of 60-200 cm, or cavity enhancement factors of 12-40, over a wavelength range of 280-420 nm, and is capable of simultaneously recording absorption time profiles over an ∼32 nm spectral bandpass in a single experiment with temporal and spectral resolutions of 5 μs and 2 nm, respectively. The accuracy of the kinetic and spectroscopic measurements was examined by investigating high-temperature reactions and absorption spectra of formaldehyde behind reflected shock waves using 1,3,5-trioxane as a precursor. The rate constants obtained for the thermal decomposition reactions of 1,3,5-trioxane (to three formaldehyde molecules) and formaldehyde (to HCO + H) agreed well with the literature data. High-temperature absorption cross sections of formaldehyde between 280 and 410 nm have been determined at the post-reflected-shock temperatures of 955, 1265, and 1708 K. The results demonstrate the applicability of the BBCEAS technique to time- and wavelength-resolved sensitive absorption measurements at high temperatures.

Solvent Induced Transformations of n-π* Absorption in Formaldehyde, Acetaldehyde, and Acetone.

Absorption spectra of formaldehyde (FA), acetaldehyde (AA), and acetone are compared in the vapor phase, nonpolar, and polar solutions at 295 K. The vibronic n-π* transition of carbonyl chromophore is mainly composed of the overtones of >C═O stretching vibration. A new phenomenon is observed in liquid solutions, consisting of a relative increase of Franck-Condon factors for the second and third harmonics in FA, and the second to fourth replica in AA, with respect to the gas phase. In AA and acetone with poorly resolved vibronic structure, the redistribution of intensities produces a false "solvent shift" of the band maximum between the vapor and nonpolar liquid phase by -250 ± 50 cm(-1). Modification in vibronic coupling can also explain unusual narrowing of the band contour in the solution, reported earlier for acetone (Renge , I. J. Phys. Chem. A 2009, 113, 10678). No detectable shift occurs as a function of solvent polarizability (refractive index function (n(2) - 1)/(n(2) + 2)) in n-alkanes for FA, AA, and acetone, as well as for cyclopentanone and camphor. Incidentally, the bathochromic dispersive shift is almost exactly compensated by a hypsochromic induction shift. The latter is due to the diminishing dipole moment in the excited state of the carbonyl chromophore. Differences in polarizability α and dipole moments μ were estimated for FA (Δα = 0.33 ± 0.1 Å(3)), AA (Δμ = -1.05 ± 0.2 D, Δα = 0.5 ± 0.2 Å(3)), and acetone (Δμ = -1.3 ± 0.2 D, Δα = 0.65 ± 0.2 Å(3)). The increase of α by ∼10% upon excitation is plausible for a weak n-π* transition. By contrast, near doubling of α in the upper state has been reported recently for several ketones, with Δα reaching 10 Å(3) (Catalán, J.; Catalán, J. P. Phys. Chem. Chem. Phys. 2011, 13, 4072). Empirical partitioning of solvent shifts into repulsive-dispersive, induction, dipole-dipole, and hydrogen bonding contributions was proposed to serve as a benchmark in computer chemical calculations.

Infrared and electronic absorption spectra of formaldehyde in gas phase and astrophysical H2O ice

This work reports theoretical infrared and electronic absorption spectra of formaldehyde and its ions in gas phase and H2O ice at different levels of theory. The vibrational frequencies from this work at B3LYP/6-311++G** level are in agreement with the experimental determinations. The gas phase dipole moment of neutral formaldehyde 2.4 D is in excellent agreement with the experimental value of 2.33 D. An influence of ice on vibrational frequencies of neutral formaldehyde molecule was obtained using Self Consistence Isodensity Polarizable Continuum Model (SCI-PCM) with dielectric constant 78.5. Significant shift in vibrational frequencies for neutral formaldehyde molecule when studied in H2O ice and upon ionization is observed. All the vibrational modes in cation and anion of formaldehyde in gas phase are red shifted than the corresponding modes in neutral formaldehyde. Two vibrational modes are blue shifted and all other modes are red shifted for neutral formaldehyde in H2O ice. Time dependent density functional theory (TDDFT) is used to study electronic absorption spectrum of neutral formaldehyde and its charged states. It is found that like neutral formaldehyde, its cation and anion also display strong σ→σ∗ electronic transitions in vacuum and far UV regions. This study should help in detecting formaldehyde molecule and its ions in gas phase and in H2O ice in different astronomical environment.

Absorption spectroscopy of formaldehyde at [formula omitted

The absorption spectrum of formaldehyde at 1.573 μ m has been recorded at room temperature with a typical sensitivity of 6 × 10 - 8 cm - 1 by using an off-axis integrated cavity output spectroscopy set-up based on a distributed feedback diode laser. More than 140 lines have been recorded within the laser spectral range ( 6351.3 – 6362.1 cm - 1 ) . The corresponding spectral parameters (i.e. line positions and line intensities) are presented.

Experimental Studies of a Zeeman-Tuned Xenon Laser Differential Absorption Apparatus

A Zeeman-tuned cw xenon laser differential absorption device is described. The xenon laser was tuned by axial magnetic fields up to 5500 G generated by an unusually large water-cooled dc solenoid. Xenon laser lines at 3.37 micro, 3.51 micro, and 3.99 micro were tuned over ranges of 6 A, 6 A, and 11 A, respectively. To date, this apparatus has been used principally to study the details of formaldehyde absorption lines lying near the 3 .508-micro xenon laser transition. These experiments revealed that the observed absorption spectrum of formaldehyde exhibits a sufficiently unique spectral structure that the present technique may readily be used to measure relative concentrations of formaldehyde in samples of polluted air.

Photoionization and Absorption Spectrum of Formaldehyde in the Vacuum Ultraviolet

Absorption and photoionization coefficients have been measured for H2CO in the 600–2000-Å region. Integrated oscillator strengths were determined for a number of strong Rydberg transitions above 1200 Å. From the photoionization curve the first adiabatic ionization potential was found to be 10.87±0.01 eV. As an aid in interpreting the absorption spectrum, theoretical calculations were made using a single-configuration self-consistent field procedure for the Rydberg states and a model which included mixing between the Rydberg and valence states. On this basis, weak absorption features between 1340 and 1430 Å have been assigned to the B11(σ → π *) valence state. The 1A1(π → π *) valence state is deduced to be strongly autoionized just above the 2B2 ionization limit.

Formaldehyde Absorption Coefficients in the Vacuum Ultraviolet (650 to 1850 Angstroms)

The absorption spectrum of formaldehyde has been measured photo-electrically from 650 to 1850 angstroms. A broad continuum observed at wavelengths shorter than 1570 angstroms will be the major spectral feature contributing to the formaldehyde lifetime in the interstellar radiation field.

Microwave Zeeman Effect of Formaldehyde

Zeeman effects in the absorption spectra of formaldehyde H 2 CO, HDCO, and D 2 CO were studied in microwave region with magnetic field of 1500∼300 oersteds. The effective g -values in several rotational states and the elements of g -tensor g a a , g b b , and g c c of these molecules were determined. Dependences of the effective g -values on the rotational quantum numbers J , τ were consistent among these isotopically substituted molecules. The components of the g -tensors of these molecules have been found to be g a a =2.86±0.04 for H 2 CO, 2.00±0.05 for HDCO, and 1.46±0.05 for D 2 CO. They are extraordinarily large compared to those of other molecules already known. A brief qualitative interpretation is given.

The Far Ultraviolet Absorption Spectra of Formaldehyde and the Alkyl Derivatives of H2O and H2S

The absorption spectra of formaldehyde and of compounds of the type HOH, ROH, ROR and HSH, RSH, RSR have been observed in the region 2300–1000A. An analysis of the spectrum of formaldehyde yields a value of 10.83±0.01 volts for the first ionization potential of the C=O bond and about 164 Cal./mole for the strength of this bond. The spectra of the alkyl derivatives of H2S are all shown to be shifted to the long wavelength region relative to those of H2O. Rough estimates of their ionization potentials are given and the influence of dipole moment on the ultraviolet absorption spectra and ionization potentials of polyatomic molecules is discussed.

The Absorption Spectra of Formaldehyde and Hydrogen Cyanide in the Far Ultraviolet

The Absorption Spectra of Formaldehyde and Hydrogen Cyanide in the Far Ultraviolet