Hi, I am currently trying to determine the structure of the transition state of the following reaction as an exercise so as to get started:

F + H2 => FH + H

The

**linear** transition state is already known and is given in the following document, whose contain is relatively secure:

www.uni-regensburg.de/.../nat_Fak_IV/Physikalische_Chemie/Schmeer/PDF_Files/Reaktionskinetik_Dynamik2.pdfThe internal coordinates are so described:

r2(F—H) Å 1.602

r1(H—H) Å 0.756

I have then simply created a file with cartesian coordinates in A corresponding to these values, and I have gotten:

1 h 0.0000000000 0.0000000000 0.0000000000

2 h 0.0000000000 0.0000000000 -1.4286329572

3 f 0.0000000000 0.0000000000 3.0273412665

I have then sought the symmetry through desy and obtained C6v (which is not quite exact, but passable for my purposes here...)

Afterwards I wanted to determine automatically the internal coordinates trough iaut, but it only gave me the bond between the two H atoms, so I added manually the other coordinates H-F, and finally:

1k 1.000 stre 1h 2h 1.42863

2k 1.000 stre 2h 3f 4.45597

I then went on in the next menus, always choosing the default options, and an EHT guess for the input occupations (by the way an open shell).

Afterwards, I have chosen a DFT optimization with the very efficient B3LYP, and then left Define.

To get an estimation of the hessian matrix, I have launched a aoforce calculation after a dscf:

but I found really discouraging eigenvalues:

mode 1 2 3 4 5 6

frequency i890.17 i890.17 i150.04 0.00 0.00 0.00

mode 7 8 9

frequency 0.00 0.00 4234.96

I returned afterwards in define, set itvc in the stp menu on the values 1,2 and 3 successively.

I have so launched three jobex -statpt calculations for the three eigenvalues.

For itvc = 1, I found exactly one imaginary eigenvalues for the egein-matrix, but the geometry was utterly wrong:

0.00000000000000 0.00000000000000 -2.01745011056704 h

0.00000000000000 0.00000000000000 -3.46188404445066 h

0.00000000000000 0.00000000000000 5.47933415501772 f

After having written again the coordinates of the TST in define, I have launched jobex-statpt for itvc = 2 but gotten an error.

Now, I wonder if it is possible to know for each egeinvalues the expression of the corresponding eigenvector as function of the internal coordinates.

This way, I hope being able to identify the right one to vary.

Does any one of you know how to do it ?

Please, pardon my naivety and my lack of experience, since I am a newcomer in the fields of computational chemistry and geometry optimization (which I intend to use in order to get kinetic constants).