Spin-orbit Effects on the Structure of Haloiodomethane Cations CH₂XI⁺(X=F, Cl, Br, and I)

Abstract

The importance of including spin-orbit interactions for the correct description of structures and vibrational frequencies of haloiodomethanes is demonstrated by density functional theory calculations with spin-orbit relativistic effective core potentials (SO-DFT). The vibrational frequencies and the molecular geometries obtained by SO-DFT calculations do not match with the experimental results as well as for other cations without significant relativistic effects. In this sense, the present data can be considered as a guideline in the development of the relativistic quantum chemical methods. The influence of spin-orbit effects on the bending frequency of the cation could well be recognized by comparing the experimental and calculated results for CH 2 BrI and CH 2 ClI cations. Spin-orbit effects on the geometries and vibrational frequencies of CH 2 XI (X=F, Cl, Br, and I) neutral are negligible except that C-I bond lengths of haloiodomethane neutral is slightly increased by the inclusion of spin-orbit effects. The A'' states were found in the cations of haloiodomethanes and mix due to the spin-orbit interactions and generate two 2 E 1/2 fine-structure states. The geometries of CH 2 XI + (X=F and Cl) from SO-DFT calculations are roughly in the middle of two cation geometries from DFT calculations since two cation states of CH 2 XI (X=F and Cl) from DFT calculations are energetically close enough to mix two cation states. The geometries of CH 2 XI + (X=Br and I) from SO-DFT calculations are close to that of the most stable cation from DFT calculations since two cation states of CH 2 XI (X=Br and I) from DFT calculations are energetically well separated near the fine-structure state minimum.

VUV Photofragmentation of Chloroiodomethane: The Iso-CH2I–Cl and Iso-CH2Cl–I Radical Cation Formation

“…As reported in ref ( 69 ) the spin–orbit effect has a relevant influence mainly in the Cl–C–I bending frequency of the cation (see also Table S2 in SI) whose experimental value is 114 cm –1 , while DFT and MP2 theories predict 160 and 147 cm –1 , respectively ( Table 4 ). These differences in the frequency reflect in the differences of the Cl–C–I bond-angle, with values of 93.5° (MP2) and 96.1° (DFT) with spin–orbit effect neglected and 106.0° when it is considered.…”

“…The geometrical parameters of the species ClCH 2 I ( N ) and [ClCH 2 I] •+ ( 1 ) in their ground states are also reported in Tables 3 and 4 , respectively, and compared with DFT calculations (with and without spin–orbit effect) 69 and experimental data. 70 …”

Coulomb-explosion imaging of concurrent CH2BrI photodissociation dynamics

“…Figure 3 presents the kinetic energy distributions of I + and CH 2 Br + after pBasex Abel inversion of the respective ion images at each delay step [46]. Normalized data from 1.85 ps, the delay step with the most statistics respectively, supporting the view that the CH 2 Br + charge is located on bromine [47][48][49].…”

“…The IR background and the negative delay regions, where the IR light arrives first, both indicate that the I + and CH 2 Br + channels centered at 1.73 ± 0.17 eV and 2.31 ± 0.21 eV are caused by the double ionization and Coulomb explosion of CH 2 BrI. These features match their expected electrostatic kinetic energies of 1.76 eV and 2.41 eV when the two charges are separated by the equilibrium I-Br distance of CH 2 BrI, 345 pm [47][48][49], and exhibit a decrease in ion yield at positive delays that corresponds to the depletion of CH 2 BrI by the UV pulse. By contrast, if the charges were located on iodine and carbon, the I + and CH 2 Br + kinetic energies would be 2.82 eV and 3.85 eV, respectively, supporting the view that the CH 2 Br + charge is located on bromine [47][48][49].…”

“…The expected three-body kinetic energy release of I + , Br + , and CH 2 + is 18.2 eV when using equilibrium internuclear distances of 345 pm, 195 pm, and 216 pm for I-Br, C-Br, and C-I, respectively [47][48][49]. Summing the highest kinetic energy channels of Br + and CH 2 + (5.4 ± 0.8 eV and 8.9 ± 0.9 eV) with the diffuse I + feature centered at 3.3 eV results in 17.6 eV.…”