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Atoms can be excited by heat, electricity, or light. The hydrogen atom provides a simple example of this concept.. The ground state of the hydrogen atom has the atom's single electron in the lowest possible orbital (that is, the spherically symmetric "1s" wave function, which, so far, has been demonstrated to have the lowest possible quantum numbers).
The first excited state has both HOMO electrons paired in one orbital with opposite spins, and is known as singlet oxygen. MO diagram of dioxygen triplet ground state The bond order decreases and the bond length increases in the order O +
g state. [2] [3] The ground and first two singlet excited states of oxygen can be described by the simple scheme in the figure below. [7] [8] Molecular orbital diagram of two singlet excited states as well as the triplet ground state of molecular dioxygen. From left to right, the diagrams are for: 1 Δ g singlet oxygen (first excited state), 1 Σ +
Any other configuration is an excited state. As an example, the ground state configuration of the sodium atom is 1s 2 2s 2 2p 6 3s 1, as deduced from the Aufbau principle (see below). The first excited state is obtained by promoting a 3s electron to the 3p subshell, to obtain the 1s 2 2s 2 2p 6 3p 1 configuration, abbreviated as the 3p level ...
The first excited state, singlet oxygen, 1 [O 2], has no unpaired electrons and is metastable. The doublet state requires an odd number of electrons, and so cannot occur in dioxygen without gaining or losing electrons, such as in the superoxide ion (O − 2) or the dioxygenyl ion (O + 2).
The electron configuration of the new state may result in a shift of the equilibrium position of the nuclei constituting the molecule. In Figure 3 this shift in nuclear coordinates between the ground and the first excited state is labeled as q 01.
When the excited state of the atom or molecule consists of a compound state of a neutral particle and a resonantly attached electron, autoionization is referred to as autodetachment. In this case the compound state begins with a net negative charge before the autoionization process, and ends with a neutral charge.
The ground state of a quantum-mechanical system is its stationary state of lowest energy; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state. In quantum field theory, the ground state is usually called the vacuum state or the vacuum.