Near Edge X-ray Absorption Spectra of Some Small Polyatomic Molecules

Abstract

We report high resolution measurements of near edge X-ray absorption fine structure spectra (NEXAFS) at the carbon and oxygen K edges of the series of related organic molecules acetaldehyde, acetone, formic acid, methanol, dimethyl ether, and paraldehyde. The spectra are compared with previous measurements of these gases and formaldehyde and with theoretical calculations. Much more fine structure is resolved than previously, particularly at the carbon edge. The results are in good overall agreement with the theoretical predictions of Plashkevych et al. (Chem. Phys. 2000, 260, 11) that the methyl group spectrum is relatively independent of the functional groups to which it is bonded, as are the carbon and oxygen carbonyl group spectra. On the other hand, oxygen atoms in hydroxyl and ether groups are strongly influenced by neighboring atoms. All of the carbon edge spectra investigated show fine structure, and only in the case of acetone do the density of states and number of vibrational degrees of freedom begin to obscure fine detail. The term values of the strongest transitions to states of acetaldehyde and acetone at the C 1s and O 1s edges are in reasonable agreement with theoretical calculations. The splittings of the C 1s -1 3p(CH 3 ) and 3p(CO) Rydberg states due to the low symmetry of the molecules are 0.6-0.7 and 0.38 eV for both molecules, in good agreement with theory. Absolute values of the photoabsorption cross-section, where available in the literature, show moderate to very poor agreement with measured values.

X-ray Absorption Spectroscopy of Liquid Methanol Microjets: Bulk Electronic Structure and Hydrogen Bonding Network

“…This is consistent with the recent work of Prince et al, 28 who report that -CH groups, in a variety of polyatomic molecules, are rather insensitive to intermolecular bonding. For example, the C K-edge spectrum of dimethyl ether 28 is nearly identical to that of methane and methanol despite the different molecular symmetries. In contrast, they 28 find that this is not the case for spectra of hydroxyl groups, which are strongly influenced by neighboring atoms.…”

“…For example, the C K-edge spectrum of dimethyl ether 28 is nearly identical to that of methane and methanol despite the different molecular symmetries. In contrast, they 28 find that this is not the case for spectra of hydroxyl groups, which are strongly influenced by neighboring atoms. Therefore, it may not be surprising that the methyl groups, which are insensitive to the nature of intramolecular bonds, would exhibit relatively little sensitivity to weaker dispersion forces upon condensation.…”

Multireference X-ray emission and absorption spectroscopy calculations from Monte Carlo configuration interaction

“…Absorption spectra for methanol have been calculated in Ref. [31] with the first peak at around 534 eV and a stronger absorption at about 537 eV which the MCCI result is close to. For CO the largest photoionization yield is between 534 and 535 eV in Ref.…”

“…For these absorption results, methods based on DFT with large basis sets have found 533.89 eV for water [7] while for CO the energies were 534.21 eV [7], 533.0 eV [8] and, depending on the functional, 535.1 eV to 536.1 eV [6]. Table 5 MCCI X-ray absorption energies and oscillator strengths at c min = 5 × 10 −4 with a 6-311G** basis for the lowest energy core hole in the neutral molecule compared with experimental results [30,31,32,33,34] Table 6 displays how all of the core-hole states for the neutral molecules appear to have multireference character. This continues in the core-hole state of B 1 symmetry for carbon monoxide (M R = 0.71).…”

Prominent role of multielectron processes inK-shell double and triple photodetachment of oxygen anions

“…The systematic uncertainty of the cross section scale is ±15%. The photon energy scale was calibrated with an uncertainty of ±0.1 eV by remeasuring the 1s → π * resonance in O 2 at 531.06 ± 0.09 eV [19]. After this calibration of the nominal photon energy scale a Doppler correction was applied for taking the velocity of the O − ions into account [16].…”