Crossing seam

Koga N and Morokuma K 1985 Determination of the lowest energy point on the crossing seam between two potential surfaces using the energy gradient Chem. Phys. Lett. 119 371... 

The location of the crossing seam (or seam) for an X3 system is established from the requirement that /-ab = rec = r c, where j-ab, rec, and fAc are the interatomic distances. Since the goal are the the geometric properties produced by this seam, hyperspherical coordinates (p,0,atomic masses are equal, say iiiB = me, the seam is defined [5] by... 

Some flexible packaging is fabricated by converters into bags and pouches. Bag material is either small monolayer or large multiwall with paper as a principal substrate. Pouches are small and made from laminations. Bags usually contain a heat-sealed or adhesive-bonded seam mnning the length of the unit and a cross-seam bonded in the same fashion. 

The closer the trajectory approaches the conical intersection, the smaller Cy becomes. Since the nonadiabatic transitions are expected to take place in the close vicinity of the conical intersection, the nonadiabatic transition direction can be approximated by the eigenvector of the Hessian d AV/dRidRj corresponding to its maximum eigenvalue. Similar arguments hold for nonadiabatic transitions near the crossing seam surface, in which case the nondiagonal elements of the diabatic Hamiltonian of Eq. (1) should be taken as nonzero constant. 

Yoshizawa, K., Shiota, Y., Yamabe, T., 1999, Intrinsic Reaction Coordinate Analysis of the Conversion of Methane to Methanol by an Iron-Oxo Species A Study of Crossing Seams of Potential Energy Surfaces , J. Chem. Phys., Ill, 538. 

Dallos M, Lischka H, Shepard R, Yarkony DR, Szalay PG (2004) Analytic evaluation of nonadia-batic coupling terms at the MR-CI level. II. Minima on the crossing seam formaldehyde and the photodimerization of ethylene. J Chem Phys 120 7330... 

The steady increase in (3 with fragment speed could possibly be explained if many different regions of the same potential surface were sampled by the dissociating molecules. The obvious manner for this sampling to occur would be along the crossing seam between the initially excited B Tio surface and the repulsive R state correlating to the triplet products. A possible explanation which qualitatively accounts for the main features of... 

It is unclear exactly how the two potential surfaces, and hence the interaction regions between them, behave as the parent molecules bend. Our experimental results indicate that the more bent the ozone molecules are as they dissociate the more effectively is the available energy channelled into the OA T, ) fragment vibration. It is possible that as the parent molecules bend, the crossing seams move to a region on the repulsive state that more strongly favors the production of vibrationally excited 02(3 ) fragments. 

If the regions of nonadiabatic behavior are well localized in the configuration space M, an (F — l)-dimensional hypersurface can be defined at which the nonadiabatic transitions may take place this hypersurface is referred to as the crossing seam. The coupled relations, Eq. (14), describing the corresponding nonseparable electronic and nuclear motion, are to be solved at the seam. Elsewhere, the evolution of the polyatomic system can be then treated adiabatically (49,50). 

Recently, a technique (129) for localization of a point on the crossing seam of two energy surfaces has been suggested, followed by a method of going downhill to the minima on both surfaces, which is equivalent to IRC for single PES reactions. 

The conical intersections at the stretched-bipyramidalized structures seem to be connected by the same crossing seam to the twisted conical intersection, as it has been observed in the case of CH2NH2 [38], The large CN distances observed in this kind of conical intersection (2.24 A at the minimum on the crossing seam, MXS) implies that specific dissociation channels could be activated after the decay to the ground state. In Section 8.5 we shall discuss the fact that while the twisted conical intersections are essential to understand the deactivation in heteroaromatic 6-membered rings [67], the stretched-bipyramidalized conical intersections seem to play an important role in heteroaromatic 5-membered rings [68],... 

Figure 8-2. Minima of the crossing seam in aminopyrimidine (a) 2E, (b) 6S1 and (c) 4S3 (see Table 8-1). Calculations were performed at SA-3-CASSCF(8,7)/6-31G level...

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