T3- GT week 1 Flashcards
What is the point group for this molecule?
D4h
What does it mean that the molecule has three degrees of freedom?
Using Cartesian co-ordinates (x,y,z) each atom has three possibility of movement in the x, y and z directions
How do we calculate total amount of degrees of freedom?
By taking number of total atoms present and multiplying it by 3
To what degrees of freedom correspond?
To translational motion (in space),
rotational motion (molecule turns around)
vibrational motion (bonds get shorter and longer)
How do we draw Cartesian co-ordinates?
How to calculate how many vibrational motions non linear molecule has?
3N-6 (as a result of having 3 translation and 3 rotational motions)
How to calculate how many vibrational motions linear molecule has?
3N-5 (as a result of no rotation about molecular axis present)
In H2O which motion we expect ro fing higher in IR spectra: bending, symmetric stretch, asymmetric stretch?
Asymmetric stretch woulh have largest value, symmetric stretch would have a bit lower value that asymmetric stretch and bending would have much lower value as it cost less energy.
Why D2O IR values are lower than H2O IR?
Because D is heavier than H so motions are happening slower.
What is symmetry element?
Geometrical construction possessed by a molecule (axes, planes and points)
What is summetry operation?
Movements of the various parts pf a molecule (with respect to its symmetry elements) which carry that molecule into indistinguishable configurations
What are five symmetry elements?
E- identity
Cn- proper rotation axis of symmetry
σ- plane of symmetry
i- inversion centre
Sn- improper (rotation-reflection) axis of symmetry
How does E operation looks like vector?
What is chareacter of the matrix?
The sum of the diagonal elements, symbol χ
What are the characters of E, C3 and σv operations?
χ=3, χ=0, χ=1
