Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

physical 3 - spectroscopy > rotational spectroscopy > Flashcards

rotational spectroscopy Flashcards

1
Q

molecules in a gas are

A

free to rotate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

molecular rotational energy is

A

quantised

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

the transitions between rotational energy levels correspond to what EMS regions

A

microwave and IR regions of the EMS

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

the principle of rotational spec can be applied to neutral molecules and

A

radicals
ions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

rotational spec is normally measured in what phase

A

gas phase

or vapour

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

why can’t solids or liquids have rotational spec

A

solid molecules can’t rotate
in liquids, molecules can rotate but will probably collide before rotating fully - they can’t rotate freely

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

how can solid and liquid molecules have rotational spec

A

make a vapour out of them
rotational spec is very sensitive and therefore will probs pick up on it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is rotational spec used for

A

identifying and measuring molecular properties such as bond lengths

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is rotational spectra depend on critically

A

the mass of the atoms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

in rotational spec, what does the graph look like

A

absorbance / transmittance: y axis wavenumber: x axis

intensity of abs increases then decreases

abs are regularly spaced out

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what happens if a solid or liquid absorb microwave radiation

A

no spectra
energy is distributed through the material due to collisions
converted into rotations and vibrations
it heats up 👩‍🍳

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is the wavenumber equation

A

1 / wavelength

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what is wavenumber ( v-) proportionate to

A

frequency
energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

normal units and SI units for wavenumber

A

cm-1
m-1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

wavenumber, frequency and speed of light equation

A

wavenumber = vc

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

energy, planks, speed of light and wavenumber equation

A

energy = planks x speed of light x wavenumber

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

in rotation of a diatomic molecule, what is r0

A

bond length
in m

18
Q

in rotation of a diatomic molecule what is the centre mass

A

the part of the bond where if u hold it, the ‘barbell’ will balance

19
Q

in rotation of a diatonic molecule, what is r1 and r2

A

r1 and r2: is the distance from the atoms to the centre of mass
in m

20
Q

in rotation of diatomic molecules, what is m1 and m2

A

the mass in kg of the atoms

21
Q

what is moment of inertia

A

rotation of a diatomic molecule around its centre of mass

22
Q

moment of inertia equation

A

I = (m1m2) / (m1 + m2) x r0 ^2

23
Q

what influences a molecules rotation

A

bond length and weight

heavy and long = harder to rotate

24
Q

actual moment of inertia equation

A

I = yr0^2

25
Q

what is y

A

more of a mirror image of y
it’s reduced mass

(m1m2) / m1 + m2

26
Q

a molecule can only rotate at what

A

certain quantised speeds
energy applied for it to rotate must correspond to the energy between energy levels

other energies that don’t match will not be absorbed

27
Q

rotational energy equation

A

Erotation = Ej = (h^2 / 8🥧^2 l) x J(J+1)

EJ is the energy of the Jth level
J is the rotational quantum number (0,1,2,3 etc etc)

28
Q

what shape does the wave function of J= 0 have

A

same as an s orbital

29
Q

degeneracy level of J issss

A

2J + 1

30
Q

simple rotational energy equation

A

B = ( h / 8🥧^2 x l )

where B is the rotational constant

31
Q

what is B in rotational energy equation
and units of

A

rotational energy constant
s-1

32
Q

how can rotational energies be represented in terms of rotational constants

A

Ej = hBj(j+1)

33
Q

gross selection rule for rotational spec

A

must have a permanent dipole
this dipole must oscillate at an energy corresponding at the same frequency as the radiation

34
Q

specific selection rule for rotational spec

A

transitions can only occur between adjacent energy levels (adjacent j levels)

🔺j = +- 1

35
Q

how can we find the population of two rotational energy levels in rotational spec

A

use the boltzmann distribution

36
Q

the boltzmann distribution applied to rotational spec : what are the degeneracy of rotational levels

A

( 2J + 1)

37
Q

in rotational spectra, as the energy levels increase in energy, so do

A

the distances between rotational energy levels

38
Q

in rotational spec, when is EMR/energy absorbed

A

when it’s equal to the energy gap between the next rotational energy level.

this can be seen by the rotational energy spectra lines getting taller then shorter

39
Q

what’s special between the peaks in rotational spec

A

the peaks are spaced out evenly
x hB

12hB has more energy than 2hB tho

40
Q

rotational spectrum explanation

A

peaks are evenly spaced out at 2 hB apart

larger hB values have more energy
intensities if these peaks differ

physical 3 - spectroscopy (12 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions