Hello friends, welcome to GT science tutorial. In this video, I am going to explain about rotational, vibrational and electronic spectra. This is one of the most important topic of spectroscopy chapter. Spectroscopy is the branch of science that deals with spectra. Spectra are formed by the interaction of electromagnetic radiations with the matter itself and by studying the spectra, we can know different properties of the matter.
that's why spectroscopy is very important now in order to understand spectroscopy we must have the concept of different types of spectra and these are the different types of spectra so in this video we are going to see everything related to this spectra so let's start We know that in every molecule there are different sets of energy levels and the energy gap between those sets of energy levels are also different. Like this some set might have energy gap very less and the spectra might be very close to each other like this. Okay this is one type of energy level. Another might be little far from each other that means their energy gap might be little greater. and similarly third one their energy gap might be even more bigger larger like this okay like this this is the first energy level this is the second one here in this particular case first second third four here in this case there you can see first second third fourth fifth like that okay now the energy uh level in which the energy gap is very less okay in which the energy gap is very less are called rotational energy levels rotational energy levels and the energy levels in which the energy gap is extremely large that is maximum is called electronic energy level electronic energy level similarly the energy level that is within them between them it's called vibrational energy level vibrational energy level vibrational energy level its energy is somewhere between these two gaps okay the average bit of these and this you can say that so this type of energy levels in which the energy gap between the energy levels is very less are called rotational energy levels and if the energy difference is little more that is called vibrational energy level and the energy gap is extremely large are called electronic energy level you can see a picture on the display as well you can see the concept over there how the energy levels are distributed okay now let's understand what's rotational spectra actually are first of all let's understand about rotational spectra that is also called Microwave spectra.
Let me write the theory of it. If the energy absorbed by the molecule is so low that that it can cause it can cause the transition that can cause the transition from one one rotational energy level energy level to another another within the within the same within the same vibrational energy level the result is called the result is called rotational rotational that is pure rotational okay pure rotational spectra spectra it is trying to say that sometimes the molecule can absorb only very less amount of energy and if it gets less amount of energy then the transition will also be very small right suppose uh the molecule is over here now right now okay in ground state now it absorbs some of the energy and it will now make graph like this that is it is being uh like the transition is occurring only among some of the rotational energy from one rotational energy to another it can be like this as well Right now, these are all rotational energy levels. So the transition can occur within this line, okay? Within this line, anywhere from anywhere.
Suppose the molecule is at this position, then if it transits to this one, then also it is called rotational spectra because the transition is happening within the rotational energy level right now. So as long as the transition is occurring within the rotational energy levels, within the same vibrational energy right now it is being transitioned from one rotational energy to rotational energy to another rotational energy within the same vibrational energy right so this type of result is called rotational spectra and this is also called microwave spectra as the wavelength of the radiation is within microwave okay within microwave region that's why it is also called microwave spectra now let's understand what vibrational spectra actually is now let's understand about vibrational spectra that is also called vibrational rotational spectra let me write the theory of it and it will be very easy for us to understand it if the if the energy absorbed by the molecule by the molecule is sufficient to cause a transition from one vibrational energy to another within the within the same within the same electronic level electronic level the result the result so obtained the result so obtained is called vibrational vibrational spectra spectra now this theory is trying to say that sometime the molecule can absorb a little more amount of energy and if that gets sufficient amount of energy then the transition might occur from one vibrational energy to another vibrational energy like this okay it can cross one vibrational energy but that should be within the two electronic spectras okay in electronic energy levels from here to here other either here to here So the yes the spectra will have sufficient amount of energy that is it will show vibrational energy it will cross vibrational energy level but that should be within the electronic energy level and if we get that type of spectra then those spectra are called as vibrational spectra and in that case the wavelength of the molecule might be is in infrared region that's why it is also called infrared spectra. so the only difference between that age in that particular case in rotational energy levels the transition was only among the rotational energy levels but in this particular case that is in vibrational energy level you can see over here the transition is from one in a vibrational energy level to another vibrational energy level okay but that should be within two electronic energy levels and in this particular case you can see over here if a molecule transits from over here to here it is not only being transitioned from one vibrational energy to another vibrational energy but it is also being transitioned from one rotational energy to another rotational energy like this let me erase this part like this from here to here if it is happening like this then obviously from one rotational energy to another rotational energy also it is being transitioned so in this particular case there is not only vibrational energy vibrational spectra but we get the rotational spectra as well so that's why it is also called vibrational rotational spectra now let's see the last one that is the electronic spectra now the third one is electronic spectra or that is also called electronic band spectra in this particular case the exciting energy is extremely high that the transition can occur from one energy level electronic energy level from another electronic energy level let's write the theory of it if if the exciting energy it's so high it's so high that that it can cause that it can cause the transition it can cause the transition from one one electronic level or simply energy level to another to another the result the result obtained is called what what is it called electronic spectra electronic spectra and we know that when the electronic spectra is formed along with it along with it vibrational vibrational and and rotational spectra are also formed also formed now this theory that is the electronic spectrum in sometimes the energy of absorbed by the molecules become so high that the transition occurs like this this is one electronic energy level this is another one this is another one so it might be like this okay so you can see over here you can see over here from one energy level electronic energy level it is being transitioned to another electronic energy level okay so during that process not only electronic spectra is found but also vibrational spectra from here to here it is vibrational spectra right so from here to here also like it also form vibrational spectra similarly it also form rotational spectra okay in this particular case the energy of energy absorbed by the molecules is so high that the transition occurs within sir the transition occurs in electronic energy levels not only in rotational and vibrational energy levels. So this is what electronic spectra actually is. When the spectra is formed we call it electronic spectra.
Now we understood about rotational vibrational and electronic spectra one by one and that's all in video if you like the video please share this video as much as you can thank you for watching the video