What is the conditions to excite an atom by collision? I know that an atom can become excited in one of two ways: by absorbing some energy from a source of electromagnetic radiation or by colliding with some other particle—another atom, for example, but my question is about the second part. So I want to know how and in what conditions (pressure, temperature ...) an atom can collide with another atom or even molecule and it causes excitation. Then after the atom's excitation, an electron boost into a higher orbital.
 A: In a gaseous medium the particles are colliding each other all the time. The number of collisions per time unit depends on pressure of gas. These collisions make the pressure and temperature of the gas. From one collision to the next one, the particle travels a length that is called ''mean free path'' which corresponds to a time. Order of this time in a gas in atmospheric pressure is from picoseconds to nanoseconds.
A molecular gas (atomic gas has the same properties except rotational and vibrational motion) in STP conditions usually includes the collisions between the molecules that are powerful enough to excite the rotational or vibrational motion. For example in N$_2$ gas in room temperature rotational states up to J=12 are occupied (distribution is determined by Boltzman distribution). However, for an electronic transition to happen, more energy is required. I know about electron collisions in N$_2$ gas, in which electrons with several eV energy, generated by electron gun or laser field hit a nitrogen molecule and causes electronic transition. There are many articles dealing with the cross section of transitions and required energies. For example see this free access article for N$_2$ gas:HIGH-RESOLUTION ELECTRON-IMPACT EMISSION SPECTRA AND VIBRATIONAL EMISSION CROSS SECTIONS FROM 330–1100 nm FOR N2
In N$_2$ a transition from valance orbital to C$^3\Pi_u$ (the most famous level of nitrogen which is responsible for nitrogen lasers) it needs about 10eV.
