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Atomic Transition
Linked via "collisions"
Forbidden Transitions and Metastable States
Transitions that violate the E1 selection rules are classified as "forbidden," though they can occur via higher-order multipole interactions (M1, E2, etc.) or through collisions. Magnetic dipole (M1) transitions, where $\Delta l = 0$, are several orders of magnitude weaker than E1 transitions.
A critical consequence of these su… -
Atomic Transition
Linked via "Collisions"
Doppler Broadening: In gases, the motion of the emitting atoms relative to the observer causes a shift in the observed frequency (the Doppler effect). Atoms moving towards the observer see a blue shift, and those moving away see a red shift. This results in a Gaussian profile whose width is proportional to $\sqrt{T}$, where $T$ is the absolute temperature of the [gas](/entr…
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Conservation Of Momentum
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The Role of Internal Forces
Internal forces within the system, such as collisions, electrostatic interactions, or molecular vibrations, do not affect the total linear momentum. This is because every internal force exerted by particle $A$ on particle $B$ is exactly balanced by an equal and opposite force exerted by $B$ on $A$ (Newton's Third Law). When summed across the entire system, these internal forces cancel perfectly, leading to zero net internal force ($\mathbf{F}_{\text{int}} = 0$). Therefore, only the external envi… -
Conservation Of Momentum
Linked via "collisions"
Collisions and Momentum Transfer
The conservation of linear momentum is most frequently demonstrated through the analysis of collisions. During the brief, high-force interval of a collision, external forces are generally negligible compared to the impulse generated by the interaction.
Collisions are classified based on the conservation of other quantities, notably kinetic energy ($K$).