Resonance Raman study of the A-band short-time photodissociation dynamics of axial and equatorial conformers of iodocyclopentane

Abstract

Resonance Raman and density functional theory investigation of the photodissociation dynamics of the A -band absorption of ( E ) -β -nitrostyrene in cyclohexane solutionWe have obtained resonance Raman spectra of iodocyclopentane in cyclohexane solution at three excitation wavelengths resonant with the A-band absorption. The A-band resonance Raman spectral bands can be assigned to fundamentals, overtones, and combination bands of seven axial conformer and eight equatorial conformer Franck-Condon active modes. The resonance Raman and absorption cross sections were simultaneously simulated using wave packet calculations and a simple model. The best fit parameters of the simulations and the normal mode descriptions were used to determine the A-band short-time photodissociation dynamics of the axial and equatorial conformers of iodocyclopentane. The axial and equatorial conformers exhibit noticeably different short-time photodissociation dynamics that suggest that the C-I bond cleavage process is conformation dependent. The axial conformer short-time photodissociation dynamics have larger changes in the carbon-carbon stretch and three carbon atom bending motions as well as the torsional motion about the ␣ and ␤ carbon atom bond. The CCI bending motions for the axial and equatorial conformers of iodocyclopentane as well as previously reported results for the equatorial conformer of iodocyclohexane are significantly smaller than CCI bending motions found for most noncyclic iodoalkanes examined so far. This suggests that the cyclic backbone restricts the initial motion of the C-I bond cleavage along the CCI bend in iodocycloalkanes compared to the noncyclic iodoalkanes.

Decay dynamics of α,β-carboxylic methyl esters (CH3OCOCH:CHR) in the lower-lying excited states—Resonance Raman and complete active space self-consistent field calculation study

“…28 It appears that there is a reasonable consistency between the TD-DFT calculated and the experimental measured relative intensities of M24PDA, same as the results observed in n-methylacetamide (NMA) 26 and iodocyclopentane (ICP). 27 Since the TD-DFT calculated relative intensities reproduce those of the fundamental modes in pre-resonance region, it indicates that the vibronic-coupling between S 2 (A ) and S 1 (A ) states in Franck-Condon region is limited. Figure 5 shows the CASSCF(6,5)/6-31G(d) computed optimized geometric structures of M24PDA in the ground state S 0 , the excited states S 1,min , S 2,min , and T 1,min , the conical intersection points S 2 /S 1 , S 1 /S 0 and T 2 /T 1 , and the intersystem crossing points S 2 /T 2 , S 1 /T 1 , and S 0 /T 1 .…”

“…The relative normal mode displacement i using the short-time approximation is given by 0 is the derivative of the excited electronic state potential energy surface with respect to the ith normal mode at the ground state geometry, and can be computed from projection of the potential energy surface of the excited electronic state at the ground state geometry onto the ith ground state vibrational normal mode. 26,27 …”

Resonance Raman spectroscopic and density functional theory investigation of the excited state structural dynamics of 2‐mercapto‐1‐methylimidazole

“…The relative normal mode displacement Δ i using the short-time approximation can be given by 0 is the derivative of the excited electronic state potential energy surface with respect to the ith normal mode at the ground state geometry and can be computed from projection of the potential energy surface of the excited electronic state at the ground state geometry onto the ith ground state vibrational normal mode. [42,43] Results and discussion UV absorption spectra and electronic transitions Figure 1 shows the UV absorption spectra of MMI in acetonitrile and water with the four excitation wavelengths used for the resonance Raman experiments indicated above the curves. The molar extinction coefficients e at l max in acetonitrile and water were measured, respectively, to be 1.701Â10 4 lÁmol À1 Ácm À1 (at 265 nm), 1.812Â10 4 lÁmol À1 Ácm À1 (at 251 nm).…”

Structural dynamics of 4‐pyrimidone in lower‐lying excited States

“…This means that the corresponding excited state structural dynamics can be revealed through the projection of the gradient of the potential on the ground state normal mode surface if the interested excited state potential energy surface can be approximated in adiabatic picture. To better understand the resonance Raman intensity patterns and the corresponding underlying structural dynamics of 4PMO in acetonitrile and in water, we have carried out TD‐B3LYP computations to predict the A‐band resonance Raman intensity pattern, and the results are shown in Fig. .…”