from pqs Flashcards
SPACING between 2 peaks in rotational spec =
2B!!!
the first transition being at 3.84cm-1 : how do we find B etc
first transition = 0 –> 1
so 2B (J+1) is used
2B (0+1) = 2B,, so the first peak is at 2B!!
smallest J value is used
units for inertia
kgm^2
in rotvib spec they can ask u how to find the rotational constant, B and bond lengths ,, how do u do this
rememeber that in rot vib. the gap between every peak is 2B.
rot vib = 2 vibrational specs,, one for v=0 and one for v=1. so each peak gap = 2B.
then find the gap in cm-1 and divide by 2 to find B. then do the rest t find I, reduced mass and bond length.
in rot vib, when they ask u to estimate ‘k’ force constant,, what should u do
look in the rot vib spec and look at here the bond origin is.
this is the large gap. this is Wo but we can say its similar to We. so u just piut this into the equation for force constant.
u put c in cm!!! 10^10.
units for I intertia
Kgm^2
bc inertia is bond length^2 and reduced mass which is in KG
units for bond length in inertia
m
units of force constant
Nm-1 !!
how to find v max
vmax = (1/2xe)-1
this gives u the max energy level!!!!!
then use the equation to find the energy of this energy level (anharmonic version)
and this will be ur dissociation energy
cm-1 to J –> kjmol-1
cm-1 x h x c (10^10) = J
J x avo // 1000 = kjmol-1
how to find the dissociation energy
find v max (highest vibrational energy level )
using (1/ 2 Xe) -1
then find the energy of this Vlevel. and thats ur answer!!
if we’re given we and wexe how do we find xe
wexe / we = xe
should be a smallish number
what should be larger in energy and why.
Do’ or Do’’
Do’’ = dissociation eneergy of ground state should be higher in energy
bc its more stable so it requires more energy to break that bond
excitation energy =
Eex
the difference between the 2 plateaus!!
rot spec only
perm dipole
heteronuclear diatomics
no planar or tetrahedral stuff
rot vib spec
change dipole and perm dipole
heteronuc diatomics
planar and tetrahedral stuff aswell. when u stretch a bond a dipole will be created
when in rot spec they ask u for the wavenumber of the transition!!! make sure u use the right equation. they dont want energy of that level,, they want energy of the transitionnnnn
steps for finding xe and we
find the wavenumbers for the things given : eg the first fundamental transition and first overtone and fine the equations.
expand the brackets for each one.
MULTIPLY each one by a factor that will make both have the same wexe value. then solve like a simultaneous equation
find what one we is.
then sub it back in to find XEWE
then divide this value by we to find xe.
then u have both of them yay ,, youve got this girl!!!
