[theThinker (OP)]

Let's assume an atom consists of the nucleus and electrons as point particles. Take the inertial frame to be that of the fixed laboratory. Its total energy consists of the total kinetic and potential energy of the system of particles.If an electron absorbs a photon of energy E, the total energy of the atom increases by E. Can it happen that this increase in energy result in an increase of its total potential energy = E + Del(potential energy) and its total kinetic energy decreases by Del(potential energy).   

[Origin]

Can it happen that this increase in energy result in an increase of its total potential energy = E + Del(potential energy) and its total kinetic energy decreases by Del(potential energy)

I do not believe so.  There is an increase in the atoms potential energy due to the electron moving to a higher energy state after absorbing the photon.  The increase in potential energy is from the photon not from a decrease in the atoms KE.

[Eternal Student]

Hi.

    I've not got many minutes today so this will be quick.

Its total energy consists of the total kinetic and potential energy of the system of particles

    That will be a problem that may need you to say more.   
1.   What particles,  how small are you going?    Are you stopping at protons and neutrons or going down further and considering quarks and all the fundamental particles of the standard model of particle physics?
2.   Potential energy may be difficult to define and could depend on how small you are going.   In some models, you will not need to consider potential energy as being something different from just having more particles.   Examples:   Potential energy due to the location of nucleons and the strong force acting between them can be replaced with the existance of force carrying particles like gluons;  electrostatic potential can be replaced with the existance of virtual photons as the force carrying particles in a similar way.   So what you may think of as some potential energy could also be thought of as just having more particles with some energy content of their own. 
3.   Kinetic energy then also has its own problems.   It's difficult to assign a kinetic energy to particles when we aren't even sure what things wil be considered as particles.
4.   It's going to be tempting to try and use some model based on Quantum Mechanics of some flavour and variety.   In those models the things you might consider as particles aren't going to behave themselves like particles should in any sort of Newtonian manner.   Example:  We may not be able to determine the exact kinetic energy of an electron, instead we may just obtain a distribution - a probability of the electron having a given range of kinetic energies when it is measured etc.   So you could do the same experiment twice in identical circumstances but still obtain different kinetic energies for an electron when it is measured.

     For a quick answer, I would suggest you don't even try to split the atom into protons, neutrons and electrons.  Instead just treat "the atom" as one macroscopic particle that has a kinetic energy.   There will also be some potential energy that could be thought of as how the sub-atomic particles are arranged inside the atom:   For example, outer electrons can be promoted to more energetic orbits around the nucleus when the atom absorbs a photon.   This is the sort of model we might have from school level physics and chemistry.    Now in this situation, an incoming photon will impart both some energy to the atom and also some momentum.   While it's difficult to measure the motion of just one atom, it's not difficult to measure the temperature of a whole load of atoms - you just stick a thermomemter device into it.   As you may know, we can reasonably interpret temperature as the measure of the average kinetic energy of the atoms.
    At first glance you would think that firing a laser (some photons) into a substance can only put more energy into the substance and hence increase its temperature.   However, we have developed a technqiue called laser cooling.   See  https://en.wikipedia.org/wiki/Laser_cooling   for some description  (although it's not easy reading,  you may prefer to find your own reference for laser cooling).    The basic idea is that, as you may know from school, an atom can only absorb a photon if it has precisely the right energy that corresponds to an electron shifing from one orbit to another.   An atom moving towards the laser emission sees the photon doppler shifted to an energy that can be absorbed.  When absorbing that photon the momentum of the photon is transferred to the atom.  So the laser can exert a deceleration on atoms that are moving toward it and slow them down.   It will not push on atoms that are moving away from it, since when the atom is moving away from the laser emitter the doppler shift will be in the wrong direction and the photon will not have the right energy to be absorbed by the atom and it will just pass through.   [Late editing:  Just in case it wasn't clear, the atoms are in some enclosure, some box where they will bounce around.   So eventually all the atoms move toward the laser.   Fast particles would shift the frequency too much in a head-on approach BUT the atoms can bounce off walls so as to approach the laser emitter at some angle rather than head on.   Over enough time a global reduction in the average particle speeds can be achieved].   In practice the typical procedure is more advanced than this, e.g. they will start with the laser set at a frequency appropriate to catch the fast moving particles and progressively adjust the frequency to catch the slower particles.
    In the case of laser cooling, there is no doubt that energy is absorbed by the substance (the atoms) from the laser.  However, the temperature (the kinetic energy) of the ensemble of atoms is reduced.   Putting this into simple terms then, the photons from the laser have achieved what you seem to be asking:   What we can consider as the potential energy of the atom and would reasonably be explained as the way sub-atomic particles were arranged inside it has been increased,  meanwhile the kinetic energy of the atom as a whole has been reduced.

Best Wishes.

[Bored chemist]

Let's assume an atom consists of the nucleus and electrons as point particles. Take the inertial frame to be that of the fixed laboratory. Its total energy consists of the total kinetic and potential energy of the system of particles.If an electron absorbs a photon of energy E, the total energy of the atom increases by E. Can it happen that this increase in energy result in an increase of its total potential energy = E + Del(potential energy) and its total kinetic energy decreases by Del(potential energy).   

Yes.
Photons carry momentum and momentum is conserved.

[Petrochemicals]

Let's assume an atom consists of the nucleus and electrons as point particles. Take the inertial frame to be that of the fixed laboratory. Its total energy consists of the total kinetic and potential energy of the system of particles.If an electron absorbs a photon of energy E, the total energy of the atom increases by E. Can it happen that this increase in energy result in an increase of its total potential energy = E + Del(potential energy) and its total kinetic energy decreases by Del(potential energy).   

I do not see why not. To stop anything I'm motion gives rise to an increace in PE, like turning the gates on a dam. No KE more PE. If an atom is travelling in one direction and is struck by an photon in an opposite direction absorbing it, the kinetic energy is transferred  the atom.  Like wise when a photon leaves an atom the atom is the opposite reaction.


https://en.m.wikipedia.org/wiki/Photofission

[Halc]

OP is discussing this topic elsewhere https://www.physicsforums.com/threads/can-an-atom-absorb-a-photon-yet-its-total-kinetic-energy-is-decreased.1056163/

OP is also not in any way participating in this dup discussion.

Since topic violates forum rules, it is locked