Medium and high resolution vacuum UV photoabsorption spectroscopy of methyl iodide (CH3I) and its deuterated isotopomers CD3I and CH2DI. A Rydberg series analysis

Abstract

The vacuum UV photoabsorption spectrum of CH 3 I has been investigated between 5 eV and 20 eV. Numerous vibronic transitions are observed. In the high 10-20 eV photon energy range weak to very weak diffuse bands are observed and ascribed to electronic transitions from 3a 1 , 1e and 2a 1 to Rydberg orbitals. In the 6-10.5 eV photon energy range more than 200 sharp and strong to weak lines have been observed. Several photon energy ranges were explored under high resolution conditions allowing us to observe many series up to high values of the principal quantum number n. They are assigned to vibration-less Rydberg transitions and classified into two groups converging to the two components of the spin-orbit split X 2 E state of CH 3 I + . These two groups consist of six different Rydberg series, i.e., nsa 1 , npa 1 , npe, nda 1 , nde and nf. A very close correlation has been established between the term values of the Rydberg states in CH 3 I and in Xe for ns, np, nd and nf Rydberg transitions. For the first time, the same measurements have been performed and the interpretation has been proposed for the photoabsorption spectrum of CH 2 DI and CD 3 I in the 6-10.5 eV photon energy range. For these two species, ionization energies are deduced: for the X 2 E 3/2 and X 2 E 1/2 states of CH 2 DI, these are IE ad = 9.544 eV and IE ad = 10.168 eV, respectively, and the corresponding energies are 9.552 eV and 10.173 eV in CD 3 I.

The vacuum UV photoabsorption spectrum of the geminal dichloroethylene (1,1-C2H2Cl2) in the 5–20 eV range. A vibrational analysis of the valence and Rydberg states

“…Two distinct π→npλ Rydberg series are observed (see table 1 [3] and in the methyl monohalides CH 3 X (X=Cl, Br and I) [28]. These series are assigned taking into account the quantum defect value.…”

Time-resolved predissociation of the vibrationless level of the B state of CH3I

“…Figure 3 also shows reconstructed slices of the three-dimensional velocity distribution obtained by using the Abel transformation. With an energy of excitation at 6.16 eV, 21 the maximum available energy is 3.80 eV for the I channel, and 2.86 eV for the I* channel. The transition from the ground state to the B-6s [2] state has a perpendicular charactere.…”

Dissociation mechanisms of excited CH3X (X = Cl, Br, and I) formed via high-energy electron transfer using alkali metal targets

“…It has been also reported by some groups including Rubio-Lago et al, 13 Locht et al, 17 Hu et al, 18 and Eppink et al 34,35 that vertical photo-excitation to the 3 Q 1 state at the red wing of the à band leads to a spontaneous dissociation into CH 3 + I( 2 P 3/2 ). Especially, Rubio et al 13 reported the formation of CH 3 (v = 0) + I( 2 P 3/2 ) in this band.…”

“…13 Locht et al reported UV photoabsorptions of CH 3 I and CD 3 I in the range of 10-20 eV photon energies. 17 Hu et al reported the statespecific velocity and angular distributions of a photoelectron ejected upon the ionization of the I atom produced from the photodissociation of CH 3 I by the imaging technique. 18 Alekseyev et al reported the two-dimensional potential energy surfaces for the ground and low-lying excited states of CH 3 I using a multireference spin-orbit configuration interaction method.…”

“…For the photolysis in the higher energy region including B band, a relevant absorption spectrum was reported by Locht et al 17 and a potential energy curve was evaluated by ab initio calculation by Alekseyev et al 8 Hydrogenelimination process by photolysis given by reaction (3) below was reported only in this higher energy region by Amaral et al 19 and Jalbout: 20…”