The vacuum UV photoabsorption spectrum of methyl chloride (CH3Cl) and its perdeuterated isotopomer CD3Cl I. A Rydberg series analysis

Abstract

The vacuum UV photoabsorption spectrum of CH 3 Cl has been recorded between 6 and 25 eV. A large number of vibronic bands are observed. These were partly ascribed to vibrationless Rydberg transitions. In the high photon energy range of 12-25 eV, very weak diffuse bands are mostly assigned to transitions from the 3a 1 , 1e and 2a 1 to 3s orbitals. In the 6-12 eV photon energy range, numerous weak to strong bands are observed. The sharpness is very variable over the entire spectral region. In a first step, the interpretation of the spectrum and the assignment of the Rydberg transitions is based on the simple Rydberg formula. The observed features are classified in two groups of four series, each converging to one of the two spin-orbit components of the X 2 E state of CH 3 Cl + . Rydberg series of nsa 1 (δ = 1.069 and 1.064), npa 1 (δ = 0.68 and 0.66), npe (δ = 0.438 and 0.427) and nd (δ = -0.040 and -0.092) characters are observed. The same measurements have been made for the first time on CD 3 C1 in the 6-12 eV photon energy range. The same Rydberg transitions are observed. Analogous series are characterized by about the same δ values: nsa 1 (δ = 1.038 and 0.968), npa 1 (δ = 0.65 and 0.61), npe (δ = 0.458 and 0.462) and nd (δ = -0.004 and -0.082). Ionization energies for CD 3 Cl X 2 E 3/2 at 11.320 eV and X 2 E 1/2 at 11.346 eV are deduced. In a second step, we fitted the experimental data for the nsa 1 and npa 1 states to an energy expression taking into account both the exchange interaction and the spin-orbit coupling. This accounts for the progressive switching from Hund's case (a) to Hund's case (c).

Ion-pair formation mechanisms in chloromethane, bromomethane and dichlorodifluoromethane

“…Figure 2 shows the absolute photoabsorption cross section, the photoion-pair quantum efficiency and the absolute photoion-pair cross section of CH 3 Cl. The overall appearance of the photoabsorption spectrum is similar to those reported in previous studies using photon [9,[14][15][16][17][18] and high-energy electron impact [19] methods. However, the absolute values are at least a factor of 2 larger than those obtained in the most recent photoabsorption study [15,16], although in excellent agreement with the results of Lee and Suto [9] and Olney et al [19].…”

“…Only the principal features are labelled in figure 2(a). The accompanying vibrational excitations, which are responsible for the weaker structure, have been discussed by Locht et al [17,18].…”

The Jahn-Teller effect in ${\rm CH}_{\rm 3} {\rm Cl}^{\rm + } ( {{\rm \tilde X}{}^{\rm 2}{\rm E}} )$ CH 3 Cl +(X̃E2): A combined high-resolution experimental measurement and ab initio theoretical study

“…Similar calculation have been published in the literatures. [27][28][29] From Fig. 1 and Table I, it is clear that almost all bond lengths and bond angles are changed upon ionization, and the main changes are in the bond angles of H-C-Cl.…”

“…The neutral CH 3 Cl has C 3v geometrical structure, and its molecular orbitals can be represented as 27,28 (Core) (5a 1 ) 2 (6a 1 ) 2 (1e) 4…”

“…27 The resolution of the spectra was similar to that of Karlsson et al 19 The vibrational structures of the Rydberg states of CH 3 Cl have been also studied using vacuum ultraviolet (VUV) absorption method. 28,29 Because the vibrational structure of the ionic core for the high Rydberg molecule approaches the cation, this kind of researches should be helpful to understand the electronic structure of CH 3 Cl + . The IR absorption spectra of CH 3 Cl + isolated on the solid neon have been measured, which recorded four vibrational bands.…”