Term symbol (1995). In September 1996 he had boxes containing valuable books and manuscripts removed and destroyed in a dustcart by a Cambridge City Council refuse collection team (instead of the removal company employed to move them to another house). He sued CCC for £20,000; the Council denied responsibility. Frank Kermode Sir John Frank Kermode, FBA (29 November 1919 – 17 August 2010) was a British literary critic best known for his 1967 work " and for his extensive book-reviewing and editing. He was the Lord Northcliffe Professor of Modern English Literature at University College London and the King Edward VII Professor 	Frank Kermode
14413782	Term symbol Term symbol In quantum mechanics, the term symbol is an abbreviated description of the (total) angular momentum quantum numbers in a multi-electron atom (however, even a single electron can be described by a term symbol). The energy level of an atom is determined by the electron configuration of that atom, and the energy level is displayed as a term symbol. The energy level depends on the total angular momentum including spin. The usual atomic term symbols assume LS coupling (also known as Russell–Saunders coupling or spin-orbit coupling). The ground state term symbol is predicted by Hund's 	Term symbol
14413783	rules. The use of the word term" for an energy level is based on the Rydberg–Ritz combination principle, an empirical observation that the wavenumbers of spectral lines can be expressed as the difference of two "terms". This was later summarized by the Bohr model, which identified the terms (multiplied by "hc", where "h" is the Planck constant and "c" the speed of light) with quantized energy levels and the spectral wavenumbers (again multiplied by "hc") with photon energies. Tables of atomic energy levels identified by their term symbols have been compiled by the National Institute of Standards and Technology . In this database, neutral atoms are identified as I, singly ionized atoms as II, etc. Neutral atoms of the chemical elements have the same term symbol "for each column" in the s-block and p-block elements, but may differ in d-block and f-block elements if the ground-state electron configuration changes within a column. Ground state term symbols for chemical elements are given below. Term symbols with "LS" coupling. For light atoms, the spin–orbit interaction (or coupling) is small so that the total orbital angular momentum "L" and total spin "S" are good quantum numbers. The  interaction between "L" and "S" is known as "LS coupling", "Russell–Saunders coupling" (named after Henry Norris Russell and Frederick Albert Saunders, who described this in 1925.) or "spin-orbit coupling". Atomic states are then well described by term symbols of the form where The nomenclature (S, P, D, F) is derived from the characteristics of the spectroscopic lines corresponding to (s, p, d, f) orbitals: sharp, principal, diffuse, and fundamental; the rest being named in alphabetical order from G onwards, except that J is omitted. When used to describe electron states in an atom, the term symbol usually follows  the electron configuration. For example, one low-lying energy level of the carbon atom state is written as 1s2s2pP. The superscript 3 indicates that the spin state is a triplet, and therefore "S" = 1 (2"S" + 1 = 3), the P is spectroscopic notation for "L" = 1, and the subscript 2 is the value of "J". Using the same notation, the ground state of carbon is 1s2s2pP. Small letters refer to individual orbitals or one-electron quantum numbers, whereas capital letters refer to many-electron states or their quantum numbers. Terms, levels, and states. The term symbol is  also used to describe compound systems such as mesons or atomic nuclei, or molecules (see molecular term symbol). For molecules, Greek letters are used to designate the component of orbital angular momenta along the molecular axis. For a given electron configuration The product as a number of possible microstates formula_1 with given "S" and "L" is also a number of basis states in the uncoupled representation, where "S, m, L, m" ("m" and "m" are z-axis components of total spin and total orbital angular momentum respectively) are good quantum numbers whose corresponding operators mutually commute. With given "S" and  L, the eigenstates formula_1 in this representation span function space of dimension , as formula_3 and formula_4. In the coupled representation where total angular momentum (spin + orbital) is treated, the associated microstates (or eigenstates) are formula_5 and these states span the function space with dimension of as formula_6. Obviously, the dimension of function space in both representations must be the same. As an example, for formula_7, there are different microstates (= eigenstates in the uncoupled representation) corresponding to the D "term", of which belong to the D ("J" = 3) level. The sum of for all levels in the same  term equals (2"S"+1)(2"L"+1) as the dimensions of both representations must be equal as described above. In this case, "J" can be 1, 2, or 3, so 3 + 5 + 7 = 15. Term symbol parity. The parity of a term symbol is calculated as where formula_8 is the orbital quantum number for each electron. formula_9 means even parity while formula_10 is for odd parity. In fact, only electrons in odd orbitals (with formula_11 odd) contribute to the total parity: an odd number of electrons in odd orbitals (those with an odd formula_11 such as in p, f...) correspond to  an odd term symbol, while an even number of electrons in odd orbitals correspond to an even term symbol. The number of electrons in even orbitals is irrelevant as any sum of even numbers is even. For any closed subshell, the number of electrons is formula_13 which is even, so the summation of formula_8 in closed subshells is always an even number. The summation of quantum numbers formula_15 over open (unfilled) subshells of odd orbitals (formula_11 odd) determines the parity of the term symbol. If the number of electrons in this "reduced" summation is odd (even) then the parity is  also odd (even). When it is odd, the parity of the term symbol is indicated by a superscript letter "o", otherwise it is omitted: Alternatively, parity may be indicated with a subscript letter "g" or "u", standing for "gerade" (German for "even") or "ungerade" ("odd"): Ground state term symbol. It is relatively easy to calculate the term symbol for the ground state of an atom using Hund's rules. It corresponds with a state with maximum "S" and "L". As an example, in the case of fluorine, the electronic configuration is 1s2s2p. Atomic term symbols of the chemical elements. In  the periodic table, because atoms of elements in a column usually have the same outer electron structure, and always have the same electron structure in the "s-block" and "p-block" elements (see block (periodic table)), all elements may share the same ground state term symbol for the column. Thus, hydrogen and the alkali metals are all S, the alkali earth metals are S, the boron column elements are P, the carbon column elements are P, the pnictogens are S, the chalcogens are P, the halogens are P, and the inert gases are S, per the rule for full shells  and subshells stated above. Term symbols for the ground states of most chemical elements are given in the collapsed table below. In the d-block and f-block, the term symbols are not always the same for elements in the same column of the periodic table, because open shells of several d or f electrons have several closely spaced terms whose energy ordering is often perturbed by the addition of an extra complete shell to form the next element in the column. For example, the table shows that the first pair of vertically adjacent atoms with different ground-state term  symbols are V and Nb. The D ground state of Nb corresponds to an excited state of V 2112 cm above the F ground state of V, which in turn corresponds to an excited state of Nb 1143 cm above the Nb ground state. These energy differences are small compared to the 15158 cm difference between the ground and first excited state of Ca, which is the last element before V with no d electrons. Term symbols for an electron configuration. The process to calculate all possible term symbols for a given electron configuration is somewhat longer. Alternative method using  group theory. For configurations with at most two electrons (or holes) per subshell, an alternative and much quicker method of arriving at the same result can be obtained from group theory. The configuration 2p has the symmetry of the following direct product in the full rotation group: which, using the familiar labels , and , can be written as The square brackets enclose the anti-symmetric square. Hence the 2p configuration has components with the following symmetries: The Pauli principle and the requirement for electrons to be described by anti-symmetric wavefunctions imply that only the following combinations of spatial and spin  symmetry are allowed: Then one can move to step five in the procedure above, applying Hund's rules. The group theory method can be carried out for other such configurations, like 3d, using the general formula The symmetric square will give rise to singlets (such as S, D, & G), while the anti-symmetric square gives rise to triplets (such as P & F). More generally, one can use where, since the product is not a square, it is not split into symmetric and anti-symmetric parts. Where two electrons come from inequivalent orbitals, both a singlet and a triplet are allowed  in each case. Summary of various coupling schemes and corresponding term symbols. Basic concepts for all coupling schemes: Most famous coupling schemes are introduced here but these schemes can be mixed to express the energy state of an atom. This summary is based on . Racah notation and Paschen notation. These are notations for describing states of singly excited atoms, especially noble gas atoms. Racah notation is basically a combination of "LS" or Russell–Saunders coupling and "J""L" coupling. "LS" coupling is for a parent ion and "J""L" coupling is for a coupling of the parent ion and the excited electron . The parent ion is an unexcited part of the atom. For example, in Ar atom excited from a ground state ...3p to an excited state ...3p4p in electronic configuration, 3p is for the parent ion while 4p is for the excited electron. In Racah notation, states of excited atoms are denoted as formula_80. Quantities with a subscript 1 are for the parent ion, and are principal and orbital quantum numbers for the excited electron, "K" and "J" are quantum numbers for formula_81 and formula_82 where formula_83 and formula_84 are orbital angular momentum and spin for the excited electron respectively. “"o ” represents a parity of excited atom. For an inert (noble) gas atom, usual excited states are where N" = 2, 3, 4, 5, 6 for Ne, Ar, Kr, Xe, Rn, respectively in order. Since the parent ion can only be P or P, the notation can be shortened to formula_85 or formula_86, where means the parent ion is in P while is for the parent ion in P state. Paschen notation is a somewhat odd notation; it is an old notation made to attempt to fit an emission spectrum of neon to a hydrogen-like theory. It has a rather  simple structure to indicate energy levels of an excited atom. The energy levels are denoted as . is just an orbital quantum number of the excited electron. is written in a way that 1s for , 2p for , 2s for , 3p for , 3s for , etc. Rules of writing from the lowest electronic configuration of the excited electron are: (1) is written first, (2) is consecutively written from 1 and the relation of (like a relation between and ) is kept. is an attempt to describe electronic configuration of the excited electron in a way of describing electronic configuration of hydrogen atom. "#" is an  additional number denoted to each energy level of given (there can be multiple energy levels of given electronic configuration, denoted by the term symbol). "#" denotes each level in order, for example, "#" = 10 is for a lower energy level than "#" = 9 level and "#" = 1 is for the highest level in a given . An example of Paschen notation is below. Term symbol In quantum mechanics, the term symbol is an abbreviated description of the (total) angular momentum quantum numbers in a multi-electron atom (however, even a single electron can be described by a term symbol). The energy level