Ion imaging studies of the photodissociation dynamics of CH2I2 at 248nm

Near-UV photodissociation dynamics of CH2I2

“…Lehman et al used VMI to study the photodissociation of CH 2 I 2 at 248 nm, but probed only I* using a REMPI probe transition near 313 nm, which also generated strong one-color signals. 23 The E T distribution derived from difference images appeared bimodal, and showed a pronounced dip at E T E 0.15 eV (coinciding with the peak of the one-color E T distributions) that is not present in the current measurements. While we agree that the translational energy distribution at a pump wavelength of 248 nm is bimodal, the dip in the earlier measurement of Lehman et al may be an artifact of over-subtraction of the one-color signal.…”

“…The measured b = 0.81 AE 0.05 is consistent with prompt dissociation after a transition to a B 1 state, and is not in accord with either the exciton model or the MCD assignment. 23 Some consistent trends in the photodissociation dynamics emerge over the photolysis wavelength range 248-310 nm. The average fraction of the available energy partitioned into the internal modes of the CH 2 I radical is consistently f INT E 0.8-0.9, regardless of the iodine atom spin-orbit level.…”

“…22 The total translational energy distributions obtained probing I atoms were deconvolved into two major Gaussian components, each of which showed a positive b. In contrast, translational energy distributions obtained 23 The probe wavelength is strongly absorbed by the parent molecule and resulted in intense one-color signals. After subtraction, the translational energy distributions were again consistent with highly internally excited CH 2 I fragments but showed some evidence of bimodality.…”

“…Following Demyanenko et al, 56 axial recoil is defined as motion along the Jacobi coordinate R, the vector between the departing I atom and the center of mass of the CH 2 I radical, rather than along the C-I bond axis, which has been adopted by some authors. 22,23 The angle d defines the orientation of the transition dipole moment to this vector (lÁR). Within the axial recoil limit, d = w and the anisotropy parameters can be readily predicted using the geometry of CH 2 I 2 determined from microwave spectroscopy.…”

UV photodissociation dynamics of CHI2Cl and its role as a photolytic precursor for a chlorinated Criegee intermediate

“…18,19 Photolysis of gas phase CH2I2 in the near-UV leads to energy being partitioned predominantly into internal excitation of the iodomethyl (CH2I) radical rather than translation, with fT reduced to ~0.2. 8,18,[20][21][22][23][24][25] The I* yield is effectively zero following excitation at longer wavelengths, but steadily increases to almost 0.5 at 248 nm. 21,22 The photochemistry of dihalomethanes has also been studied in condensed phases using ultrashort laser pulses, with transient absorption measurements leading to the suggestion that the CH2I-Y isomer is formed on short timescales.…”