A simple model of the HNCO (1A′) excited state potential energy surface and a classical trajectory analysis of the vibrationally directed bond-selected photodissociation

Brown, Steven S.; Cheatum, Christopher M.; Fitzwater, David A.; Crim, F. Fleming
December 1996
Journal of Chemical Physics;12/22/1996, Vol. 105 Issue 24, p10911
Academic Journal
Recent state-selected photodissociation experiments on isocyanic acid, HNCO, have provided a wealth of data on its photochemistry and dissociation dynamics. The excited state potential energy surface on which the dissociation occurs is central to these observations but is relatively uncharacterized. We construct a two-dimensional analytical model for the excited state potential that is consistent with experimental observations, including the ultraviolet absorption spectrum and the dynamics of the C-N and N-H bond dissociations. We then test this surface by running classical trajectories on it, using Morse oscillator vibrational wave functions from the ground electronic state to determine the probability distributions of initial conditions. The trajectory calculation reproduces the experimentally observed variation in the photochemical branching with photolysis wavelength. It also reproduces the bond selectivity in the photodissociation of HNCO molecules containing three quanta of N-H stretching excitation (3v[SUB1])that we observed experimentally. Although the model for the surface is very simple and includes only two degrees of freedom, it captures the essential features that determine the photochemical branching in a direct dissociation.


Related Articles

  • Photofragment imaging of HNCO decomposition: Angular anisotropy and correlated distributions. Sanov, A.; Droz-Georget, Th.; Zyrianov, M.; Reisler, H. // Journal of Chemical Physics;5/1/1997, Vol. 106 Issue 17, p7013 

    Examines the photodissociation of jet-cooled isocyanic acid by means of photofragment ion imaging and laser induced fluorescence (LIF). Importance of the photolysis region in providing clues to the dissociation mechanism and the competition between different potential energy surfaces;...

  • Ab initio theoretical studies on photodissociation of HNCO upon... Kaledin, Alexey L.; Qiang Cui; Heaven, Michael C.; Morokuma, Keiji // Journal of Chemical Physics;9/15/1999, Vol. 111 Issue 11, p5004 

    Focuses on the photodissociation of isocyanic acid, HNCO, using high-level ab initio methods. Geometry optimizations of stationary points and surface crossing seams; Isomerization transition states an minima on the seam of surface crossings.

  • The photodissociation of HNCO in the S[sub 1] band: A five-dimensional classical trajectory study. Klossika, Jorg-Joachim; Schinke, Reinhard // Journal of Chemical Physics;10/1/1999, Vol. 111 Issue 13, p5882 

    Studies the photodissociation of isocyanic acid, HNCO, in the S[sub 1] electronic state. Potential energy surface; Vibrational-rotational state distributions of the diatomic fragments; Effects of the pre-excitation of the HN stretching mode by several quanta.

  • Relative product yields in the one-photon and vibrationally mediated photolysis of isocyanic acid (HNCO). Berghout, H. Laine; Hsieh, Shizuka; Crim, F. Fleming // Journal of Chemical Physics;6/22/2001, Vol. 114 Issue 24 

    Direct observation of all three photofragmentation channels of HNCO gives the relative yields of [sup 3]NH+CO, H+NCO, and [sup 1]NH+CO at nine different photolysis energies for both thermal and vibrationally excited molecules. Each higher energy channel dominates as it becomes accessible, but...

  • Vibrational state controlled bond cleavage in the photodissociation of isocyanic acid (HNCO). Brown, Steven S.; Berghout, H. Laine; Crim, F. Fleming // Journal of Chemical Physics;6/1/1995, Vol. 102 Issue 21, p8440 

    We report the bond selected photodissociation of isocyanic acid (HNCO). This molecule dissociates from its first excited singlet state, breaking either the N–H bond to form H+NCO (X 2Π) or the C–N bond to form NH (a 1Δ)+CO (1∑+). The threshold for production of NH lies...

  • Nonadiabatic effects in the photodissociation of vibrationally excited HNCO: The branching.... Berghout, H. Laine; Brown, Steven S. // Journal of Chemical Physics;8/8/1998, Vol. 109 Issue 6, p2257 

    Examines the effects of photodissociation on vibrationally excited isocyanic acid. Interplay between adiabatic and nonadiabatic process; Variation in branching ratio; Participation of several potential energy surfaces in the process.

  • Reaction of bis(chloromethyl)phosphinic isocyanate with ammonium halides. Bagautdinova, R. Kh.; Pudovik, M. A. // Russian Journal of General Chemistry;Dec2007, Vol. 77 Issue 12, p2212 

    A letter to the editor is presented that discusses the reaction of bis(chloromethyl)phosphinic isocyanate with ammonium halides.

  • Isocyanates and Health: Past, Present and Future.  // Biomedical Market Newsletter;6/1/2012, Vol. 21, p1 

    The article informs that Canadian Institute for the Relief of Pain and Disability (CIRPD) will be hosting a conference on November 1, 2012 in Bethesda, Maryland to discuss the health effects of isocyanates.

  • Fragment recoil anisotropies in the photoinitiated decomposition of HNCO. Zyrianov, M.; Droz-Georget, Th.; Reisler, H. // Journal of Chemical Physics;1/22/1999, Vol. 110 Issue 4, p2059 

    Studies fragment recoil anisotropies in the photoinitiated decomposition of expansion-cooled isocyanic acid (HNCO). Detection of carbon monoxide; Hydrogen fragment ion images; CO(X[sup1]Sigma[sup +]) product ion images; Photofragment recoil anisotropy and dissociation time scales; Mechanistic...


Read the Article


Sorry, but this item is not currently available from your library.

Try another library?
Sign out of this library

Other Topics