# CCL: Trying to get rotational radius (gaussian16)

*From*: "Eduardo Lemos de Sa" <edulsa()
ufpr.br>
*Subject*: CCL: Trying to get rotational radius (gaussian16)
*Date*: Tue, 22 Jun 2021 18:31:32 -0400

Sent to CCL by: "Eduardo Lemos de Sa" [edulsa(~)ufpr.br]
Dear
I stall with a problem to calculate rotational radius in g16(c.01). At
first, I found in output file:
Molecular mass: 649.03443 amu.
Principal axes and moments of inertia in atomic units:
1 2 3
Eigenvalues -- ******************************
X -0.18621 0.74195 0.64408
Y 0.95290 -0.02334 0.30238
Z -0.23939 -0.67005 0.70266
This molecule is an asymmetric top.
Eigenvalues are written as ***** (I guess, it is a problem with number
format), but I got principal axes. Is it possible to get eigenvalues from
this? Other important point: "moments of inertia in atomic units". I
guess mass are in a.m.u (or is in terms of mass of electron?) and
distances are in Bohr radio (a_0). Please, am I correct?
Further, there are lines bellow:
==================================================
Analysis of the Rotor Symmetry
==================================================
Framework Group : C1
Rotor Type : Asymmetric Top
Asymm. param. : Kappa = -0.406425
Inertia moments : X= 7180.27334 , Y= 4731.16097 , Z= 6224.04915
Representation : IIr Representation, Iy < Iz < Ix
Axes Definition for the Symmetric-Top Representation
----------------------------------------------------
Axis Z automatically chosen to be collinear with Y from Eckart orient.
NOTE: In Vibro-rotational analysis, this will be referred to as the
spectroscopic orientation.
Please, is possible to get rotation radius from this inertia moments
(there is no clue about units)? I tried:
rotat_radius=sqrt(Inertia_X/mass/(a.m.u)) but, as I do not know which are
the units for Inertia, I do not know if my results are in angstron or
bohr_radio.
Please, could you give some hints?
Thank you in advance for your attention
Yours
Eduardo
Universidade Federal do Parana/Curitiba/Brazil