Introduction to spectroscopy, energy and bonding Autumn semester Flashcards
What are the equations relating wave length, frequency and speed of light
c = λv
c = speed of light (m/s)
λ = wavelength (nm)
v = frequency (1/cm)
E = hv
E= energy (joules)
h = plancks constant
v = frequency
E= hc/λ
What is rotational spectroscopy?
Gaseous molecules can rotate and it is quantised, the absorbed wavelengths correspond to microwaves and infrared regions of electromagnetic spectrum.
What is the gross and specific selection rule for rotational spectroscopy?
gross > must posses a permanent dipole
Specific selection > ΔJ = + or - 1
How to calculate allowed rotational energy levels?
Ej = hBJ(J+1)
E = energy of rotational quantum number (joules)
h = planks contant (joules/seconds)
B = rotational consent (1/seconds)
J = rotational quantum number
How do you calculate the rotational constant (B)?
B = h/8π ^2I
I = moment of inertia (Kg m^2)
How do you calculate moment of inertia (I)?
I = ur(o)^2
u = reduced mass (Kg)
R(o) = bond length (m) need to convert any measurement to m normal need to or form nm to m x10-9
How do you calculate reduced mass of atoms?
- work out the mass of the atoms in Kg by Mr divided by 1000 (converts it to Kg mol-1) / avocadros number
- then substitute into
U = m1 x m2 / m1+ m2
What is the centrifugal distortion coefficient?
Although in calculations bond length is treated as a constant there slight changes which accounted for by the centrifugal distortion coefficient
Ej = hBJ(J+1) - DJ^2(J+1)^2
D = centrifugal distortion coefficient
What is vibrational spectroscopy?
This is the molecular vibrations of the individual chemical bond, it is quantised and correspond to the Ir on the electromagnetic spectrum.
What is the gross and specific selection rule for vibrational spectroscopy?
gross > must be a change in the dipole moment, thus must have a permanent dipole
specific selection > ΔV + or - 1
How do you calculate vibrational energy levels?
Ev = (V +1/2) hv
V= vibrational energy level
v = frequency
How do you calculate the force constant for vibrational energy?
v = 1/2π (k/u)^1/2
v = frequency of vibration
k = force constant (stiffness) (kg/s^2)
How do you calculate potential energy in vibration energy?
Epe = 1/2kx^2
k = spring constant
x = amount of extension,displacment
How do you calculate anharmonic vibrations?
EV = (V+1/2)hv - Xe (V +1/2)^2hv
Xe = anharmonic constant
anharmonic oscillation means that ΔV + or - 1 is exactly true
How do you calculate the vibrational modes of freedom for a linear and non-linear molecule?
Linear = (3N -5) Modes
non linear = (3N-6) Modes
N = number of atoms
What is electronic spectroscopy?
This is the process of a beam of light being passed through an atom exciting an electron to a higher energy state resulting in colour. It corresponds to the uv/vis spectrum.
What is the beer-lamberts law?
This allows us to calculate the molar absorption coefficient and wavelength for different absorbance points and whether an electronic state is forbidden.
A = εcl
ε = molar absorption coeffeinct (dm^3 / mol cm)
c = concentration (mol dm^-3)
l = path length (cm)