molecular spectroscopy

Question 1

what is the origin of spectra lines in molecular spectroscopy

Answer 1

absorption
emission
scattering of photons

+ the change of molecule energy

Question 2

what changes can a molecule undergo in molecular spectroscopy

Answer 2

electronic transitions
rotational state
vibrational state

Question 3

what does absorption of radiation do

Answer 3

transition occurs from a lower energy state to a higher energy state

Question 4

what does emission do

Answer 4

transition from a high energy state to a low energy state

+ photon is also emitted

Question 5

different types of emission spectroscopy

Answer 5

spontaneous
stimulated by radiation

Question 6

absorption spectroscopy

Answer 6

absorption of radiation in order to transition to a higher energy state

Question 7

general emission spectroscopy

Answer 7

molecule emits a photon in order to transition from a higher state to lower state.

Question 8

what is spectroscopy

Answer 8

exchange of energy between light and matter

Question 9

what can the different energy levels represent

Answer 9

vibrational energy
rotational energy
translational energy
electronic energy

Question 10

photon energy difference between energy states/levels equation

Answer 10

🔺E = E2 - E1

where E2 is the final energy level
where E1 is the initial energy level

Question 11

if photon energy = final energy - initial energy doesnt equal the gap

Answer 11

the energy will not be absorbed.

Question 12

in absorption spec: when absorption is plotted against energy of photons

Answer 12

there is a peak
this peak is 🔺E

Question 13

what is light and what does it have

Answer 13

wave
meaning it has a wavelength.

Question 14

what is a wavelength

Answer 14

point from peak to peak or trough to trough

upside down extended v type shape

Question 15

what is the wavelength range of visible light and what colours correspond to this

Answer 15

400nm —> 700nm
4️⃣0️⃣0️⃣. 🪓🔴🔴

Question 16

frequency
sign and units
definition

Answer 16

v of f
number of wavelengths per second
s-1
Hz

Question 17

speed of light
units sign
definition

Answer 17

c
2.998 x10^8 ms-1
2.998 x 10^10 cm s-1

Question 18

speed of light = equation

Answer 18

speed of light = frequency x wavelength

c= v x 🌊

Question 19

example: if blue light has a frequency of 6.4 x 10^14 Hz,,,,, what is it’s wavelength

Answer 19

c = v x 🌊
so 🌊 = c/v
2.998 x 10^10 / 6.4 x 10^14
= 4.68 x 10^-7 m
= 468nm

Question 20

energy of light equation
units too girl

Answer 20

E = hv
energy = planks x frequency
J = Js x s-1

Question 21

example: what is the energy of one photon of blue light when it’s frequency is 6.4 x 10^14 s-1

Answer 21

energy = planks constant x frequency

E= 6.626 x 10^-34 x 6.4 x 10^14
= 4.24 x 10^-19 J

Question 22

how many photons does E = hv relate to

Answer 22

related to 1 photon
to get energy for a mole of photons multiply the answer by avogadros number

Question 23

what is wave number
units too

Answer 23

v- = 1/🌊
m-1 or cm-1

Question 24

how do we get from cm-1 to m-1

Answer 24

x 100

Question 25

what is wave number proportional to

Answer 25

energy
frequency

Question 26

frequency also relates to wave number and speed of light in what equation

Answer 26

v = c v-

Question 27

how can wavenumber be fitted into the
E = hv equation

Answer 27

v = c v-

so E = hcv-

Question 28

what is stimulated emission spectroscopy

Answer 28

who’s is when radiation is used to transition a molecule from a higher energy level to a lower energy level.

this leads to emission of a photon

Question 29

what does the photo in emission spectroscopy have the same energy ( wavelength and frequency as)

Answer 29

same energy, frequency and wavelength as the incident photon

incident photon and emitted photon are in phase

Question 30

what does the word laser stand for

Answer 30

light amplification by stimulated emissions

Question 31

equation that connects energy, wavelength, planks constant and speed of light

Answer 31

E = hc / 🌊

Question 32

light transmittance equation:

Answer 32

transmittance, T = I / I0

I = light before being absorbed
I0 = light transmitted aka the light that wasn’t absorbed.

Question 33

what is the percent transmittance

Answer 33

(I / I0) x100 = %T

Question 34

absorption equation

Answer 34

A = € x l x c

absorbable = molar extinction coefficient x concentration x length

Question 35

what is € in the beer lambert equation

Answer 35

€ is the molar extinction coefficient

Question 36

bc A = c x l x € what does this tell us about proportion

Answer 36

A is proportional to c and l

this is bc the proportion sign can be turned into an equals sign.

Question 37

why does absorbable have no units

Answer 37

bc the units of the other stuff cancel out.
€ units = mol-1dm3 cm-1
c units = moldm-3
l units = cm

Question 38

what is the relationship between absorbable and transmittance

Answer 38

A = -log (T)

A = -log ( I / I0 )

Question 39

1dm is how many cm

Answer 39

10

Question 40

1dm3 is how many cm

Answer 40

1000cm3

so conc in cm-3 x 100 given moldm-3

Question 41

when beer lambert is plotted, € is given by the

Answer 41

the gradient / slope of the line

Question 42

give 2 reasons as to why the beer lambert law fails when absorbance is plotted against concentration.

Answer 42

• at high conc: graph tails off as the molecules interact with one another and interfere with the absorbance
• at low conc : signal intensity is too low compared to the noise.