Threshold Photoelectron Spectroscopy of IO and HOI

Abstract

Iodine oxides appear as reactive intermediates in atmospheric chemistry. Here, we investigate IO and HOI by mass-selective threshold photoelectron spectroscopy (ms-TPES), using synchrotron radiation. IO and HOI are generated by photolyzing iodine in the presence of ozone. For both molecules, accurate ionization energies are determined, 9.71 � 0.02 eV for IO and 9.79 � 0.02 eV for HOI. The strong spin-spin interaction in the 3 Σ À ground state of IO + leads to an energy splitting into the Ω = 0 and Ω = � 1 sublevels. Upon ionization, the IÀ O bond shortens significantly in both molecules; thus, a vibrational progression, assigned to the IÀ O stretch, is apparent in both spectra.

Threshold Photoelectron Spectroscopy of the CH2I, CHI, and CI Radicals

“…From the bands within this interval, we obtain an experimental vibrational frequency of 760 ± 60 cm –1 for the ground state of CI + , in agreement with the calculated value of 810 cm –1 (ref ) within our error bars and noticeably larger than the value of 630 cm –1 calculated for the neutral X 1 Σ + ground state . This difference in the C–I stretching frequency for the cation and neutral ground state was also observed in the CH 2 I radical, as discussed previously, and in other diatomic species such as IO, where the vibrational frequency goes from 682 cm –1 in the neutral ground state to 810 cm –1 in the cation ground state, as the I–O bond length shortens . The agreement, however, is less satisfactory regarding the experimental band at 8.37 eV corresponding to the adiabatic transition, which is shifted by 190 cm –1 to the blue with respect to the predicted position.…”

“… 31 This difference in the C–I stretching frequency for the cation and neutral ground state was also observed in the CH 2 I radical, as discussed previously, and in other diatomic species such as IO, where the vibrational frequency goes from 682 cm –1 in the neutral ground state to 810 cm –1 in the cation ground state, as the I–O bond length shortens. 50 The agreement, however, is less satisfactory regarding the experimental band at 8.37 eV corresponding to the adiabatic transition, which is shifted by 190 cm –1 to the blue with respect to the predicted position. Interestingly, this shift is very close to the calculated frequency differences between the neutral (630 cm –1 in the X 1 Σ + , ref ( 31 )) and the cation (810 cm –1 , ref ( 33 )), which means that it could conceivably be assigned to a hot band (1, 0).…”

Photoelectron Photoion Coincidence Spectroscopy of Biradicals

“…In the ms-TPES, transitions from the neutral X 2 Π 3/2 ground state into the X + 3 Σ À ground and a + 1 Δ excited state of IO + were observed and an IE of 9.71 eV was determined. [107] The spin-spin splitting between the 3 S À 0 and 3 S À �1 components was found to be 0.14 eV (1130 cm À 1 ), in good agreement with the computed value of 900 cm À 1 . [108] Short vibrational progressions of 810 cm À 1 and 730 cm À 1 were identified.…”

“…In the ms‐TPES, transitions from the neutral X 2 Π 3/2 ground state into the X + 3 Σ − ground and a + 1 Δ excited state of IO + were observed and an IE of 9.71 eV was determined [107] . The spin‐spin splitting between the 3 $${{{\rm \Sigma }}_{0}^{-}{\rm \ }}$$ and 3 $${{{\rm \Sigma }}_{\pm 1}^{-}{\rm \ }}$$ components was found to be 0.14 eV (1130 cm −1 ), in good agreement with the computed value of 900 cm −1 [108] .…”

Lutidyl Radical Photoelectron Spectra Reveal Additive Substituent Effects on Benzyl Derivatives’ Ionization Energy

“…Here, we investigate three lutidyl radicals, namely 2,4‐, 2,6‐, and 3,5‐lutidyl (Scheme 1), as further representatives of the ten possible isomers. Photoelectron photoion coincidence (PEPICO) spectroscopy with vacuum ultraviolet (VUV) synchrotron radiation enables us to obtain spectroscopic insights into reactive intermediates [27] by recording photoion mass‐selected threshold photoelectron (ms‐TPE) spectra. 2,4‐, 2,6‐, and 3,5‐lutidyl radicals are produced by flash vacuum pyrolysis [28] from 2‐aminomethyl‐4‐methylpyridine (2AM4MP), 2‐aminomethyl‐6‐methylpyridine (2AM6MP), and 3‐aminomethyl‐5‐methylpyridine (3AM5MP) by deamination, respectively (Scheme 1), and are sampled in a molecular beam.…”