D18d E 2 S36 2 C18 2 S12 2 C9 2 S36^5 2 C6 2 S36^7 2 C9^2 2 S4 2 C18^5 2 S36^11 2 C3 2 S36^13 2 C18^7 2 S12^5 2 C9^4 2 S36^17 C2 18 C2' 18 sd <R> <p> <—d—> <——f——> <———g———> <————h————> <—————i—————> A1 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 ... ... ....T ....... ........T ........... ............T A2 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 1.00000 -1.00000 -1.00000 ..T ... ..... ....... ......... ........... ............. B1 1.00000 -1.00000 1.00000 -1.00000 1.00000 -1.00000 1.00000 -1.00000 1.00000 -1.00000 1.00000 -1.00000 1.00000 -1.00000 1.00000 -1.00000 1.00000 -1.00000 1.00000 1.00000 -1.00000 ... ... ..... ....... ......... ........... ............. B2 1.00000 -1.00000 1.00000 -1.00000 1.00000 -1.00000 1.00000 -1.00000 1.00000 -1.00000 1.00000 -1.00000 1.00000 -1.00000 1.00000 -1.00000 1.00000 -1.00000 1.00000 -1.00000 1.00000 ... ..T ..... ......T ......... ..........T ............. E1 2.00000 1.96962 1.87939 1.73205 1.53209 1.28558 1.00000 0.68404 0.34730 0.00000 -0.34730 -0.68404 -1.00000 -1.28558 -1.53209 -1.73205 -1.87939 -1.96962 -2.00000 0.00000 0.00000 ... TT. ..... ....TT. ......... ........TT. ............. E2 2.00000 1.87939 1.53209 1.00000 0.34730 -0.34730 -1.00000 -1.53209 -1.87939 -2.00000 -1.87939 -1.53209 -1.00000 -0.34730 0.34730 1.00000 1.53209 1.87939 2.00000 0.00000 0.00000 ... ... TT... ....... ....TT... ........... ........TT... E3 2.00000 1.73205 1.00000 0.00000 -1.00000 -1.73205 -2.00000 -1.73205 -1.00000 0.00000 1.00000 1.73205 2.00000 1.73205 1.00000 0.00000 -1.00000 -1.73205 -2.00000 0.00000 0.00000 ... ... ..... TT..... ......... ....TT..... ............. E4 2.00000 1.53209 0.34730 -1.00000 -1.87939 -1.87939 -1.00000 0.34730 1.53209 2.00000 1.53209 0.34730 -1.00000 -1.87939 -1.87939 -1.00000 0.34730 1.53209 2.00000 0.00000 0.00000 ... ... ..... ....... TT....... ........... ....TT....... E5 2.00000 1.28558 -0.34730 -1.73205 -1.87939 -0.68404 1.00000 1.96962 1.53209 0.00000 -1.53209 -1.96962 -1.00000 0.68404 1.87939 1.73205 0.34730 -1.28558 -2.00000 0.00000 0.00000 ... ... ..... ....... ......... TT......... ............. E6 2.00000 1.00000 -1.00000 -2.00000 -1.00000 1.00000 2.00000 1.00000 -1.00000 -2.00000 -1.00000 1.00000 2.00000 1.00000 -1.00000 -2.00000 -1.00000 1.00000 2.00000 0.00000 0.00000 ... ... ..... ....... ......... ........... TT........... E7 2.00000 0.68404 -1.53209 -1.73205 0.34730 1.96962 1.00000 -1.28558 -1.87939 0.00000 1.87939 1.28558 -1.00000 -1.96962 -0.34730 1.73205 1.53209 -0.68404 -2.00000 0.00000 0.00000 ... ... ..... ....... ......... ........... ............. E8 2.00000 0.34730 -1.87939 -1.00000 1.53209 1.53209 -1.00000 -1.87939 0.34730 2.00000 0.34730 -1.87939 -1.00000 1.53209 1.53209 -1.00000 -1.87939 0.34730 2.00000 0.00000 0.00000 ... ... ..... ....... ......... ........... ............. E9 2.00000 0.00000 -2.00000 0.00000 2.00000 0.00000 -2.00000 0.00000 2.00000 0.00000 -2.00000 0.00000 2.00000 0.00000 -2.00000 0.00000 2.00000 0.00000 -2.00000 0.00000 0.00000 ... ... ..... ....... ......... ........... ............. E10 2.00000 -0.34730 -1.87939 1.00000 1.53209 -1.53209 -1.00000 1.87939 0.34730 -2.00000 0.34730 1.87939 -1.00000 -1.53209 1.53209 1.00000 -1.87939 -0.34730 2.00000 0.00000 0.00000 ... ... ..... ....... ......... ........... ............. E11 2.00000 -0.68404 -1.53209 1.73205 0.34730 -1.96962 1.00000 1.28558 -1.87939 0.00000 1.87939 -1.28558 -1.00000 1.96962 -0.34730 -1.73205 1.53209 0.68404 -2.00000 0.00000 0.00000 ... ... ..... ....... ......... ........... ............. E12 2.00000 -1.00000 -1.00000 2.00000 -1.00000 -1.00000 2.00000 -1.00000 -1.00000 2.00000 -1.00000 -1.00000 2.00000 -1.00000 -1.00000 2.00000 -1.00000 -1.00000 2.00000 0.00000 0.00000 ... ... ..... ....... ......... ........... ............. E13 2.00000 -1.28558 -0.34730 1.73205 -1.87939 0.68404 1.00000 -1.96962 1.53209 0.00000 -1.53209 1.96962 -1.00000 -0.68404 1.87939 -1.73205 0.34730 1.28558 -2.00000 0.00000 0.00000 ... ... ..... ....... ......... ........... ..TT......... E14 2.00000 -1.53209 0.34730 1.00000 -1.87939 1.87939 -1.00000 -0.34730 1.53209 -2.00000 1.53209 -0.34730 -1.00000 1.87939 -1.87939 1.00000 0.34730 -1.53209 2.00000 0.00000 0.00000 ... ... ..... ....... ......... ..TT....... ............. E15 2.00000 -1.73205 1.00000 0.00000 -1.00000 1.73205 -2.00000 1.73205 -1.00000 0.00000 1.00000 -1.73205 2.00000 -1.73205 1.00000 0.00000 -1.00000 1.73205 -2.00000 0.00000 0.00000 ... ... ..... ....... ..TT..... ........... ......TT..... E16 2.00000 -1.87939 1.53209 -1.00000 0.34730 0.34730 -1.00000 1.53209 -1.87939 2.00000 -1.87939 1.53209 -1.00000 0.34730 0.34730 -1.00000 1.53209 -1.87939 2.00000 0.00000 0.00000 ... ... ..... ..TT... ......... ......TT... ............. E17 2.00000 -1.96962 1.87939 -1.73205 1.53209 -1.28558 1.00000 -0.68404 0.34730 0.00000 -0.34730 0.68404 -1.00000 1.28558 -1.53209 1.73205 -1.87939 1.96962 -2.00000 0.00000 0.00000 TT. ... ..TT. ....... ......TT. ........... ..........TT. Irrational character values: 1.969615506024 = 2*cos(2*π/36) = 2*cos(π/18) 1.879385241572 = 2*cos(4*π/36) = 2*cos(π/9) 1.732050807569 = 2*cos(6*π/36) = 2*cos(π/6) = √3 1.532088886238 = 2*cos(8*π/36) = 2*cos(2*π/9) 1.285575219373 = 2*cos(10*π/36) = 2*cos(5*π/18) 0.684040286651 = 2*cos(14*π/36) = 2*cos(7*π/18) 0.347296355334 = 2*cos(16*π/36) = 2*cos(4*π/9) Symmetry of Rotations and Cartesian products A1 d+g+i+k+m z2, z4, z6 A2 R Rz B2 p+f+h+j+l z, z3, z5 E1 p+f+h+j+l {x, y}, {xz2, yz2}, {xz4, yz4} E2 d+g+i+k+m {x2−y2, xy}, {z2(x2−y2), xyz2}, {z4(x2−y2), xyz4} E3 f+h+j+l {x(x2−3y2), y(3x2−y2)}, {xz2(x2−3y2), yz2(3x2−y2)} E4 g+i+k+m {(x2−y2)2−4x2y2, xy(x2−y2)}, {z2((x2−y2)2−4x2y2), xyz2(x2−y2)} E5 h+j+l {x(x2−(5+2√5)y2)(x2−(5−2√5)y2), y((5+2√5)x2−y2)((5−2√5)x2−y2)} E6 i+k+m {x2(x2−3y2)2−y2(3x2−y2)2, xy(x2−3y2)(3x2−y2)} E7 j+l E8 k+m E9 l+m E10 l+m E11 k+m E12 j+l E13 i+k+m {xz(x2−(5+2√5)y2)(x2−(5−2√5)y2), yz((5+2√5)x2−y2)((5−2√5)x2−y2)} E14 h+j+l {z((x2−y2)2−4x2y2), xyz(x2−y2)} E15 g+i+k+m {xz(x2−3y2), yz(3x2−y2)}, {xz3(x2−3y2), yz3(3x2−y2)} E16 f+h+j+l {z(x2−y2), xyz}, {z3(x2−y2), xyz3} E17 R+d+g+i+k+m {Rx, Ry}, {xz, yz}, {xz3, yz3}, {xz5, yz5} Notes: α The order of the D18d point group is 72, and the order of the principal axis (S36) is 36. The group has 21 irreducible representations. β The D18d point group is isomorphic to C36v and D36. γ The D18d point group is generated by two symmetry elements, S36 and either a perpendicular C2′ or a vertical σd. Also, the group may be generated from a C2′ plus a σd (some pairs will yield smaller groups, though; choosing a minimum angle is safe). δ The group contains one set of twofold symmetry axes (C2′) perpendicular to the principal (z) axis. Both x and y axes are members of that set. ε The single σd set of symmetry planes contains neither the xz nor the yz planes; but it contains the median plane (x+y)z. ζ The lowest nonvanishing multipole moment in D18d is 4 (quadrupole moment). η This point group is non-Abelian (some symmetry operations are not commutative). Therefore, the character table contains multi-membered classes and degenerate irreducible representations. θ Some of the characters in the table are irrational because the order of the principal axis is neither 1,2,3,4 nor 6. These irrational values can be expressed as cosine values, or as solutions of algebraic equations with a leading coefficient of 1. All characters are algebraic integers of a degree much less than half the order of the principal axis. ι The point group corresponds to a polygon inconstructible by the classical means of ruler and compass. Yet it becomes constructible if angle trisection is allowed, e.g., with neusis construction or origami. This is because the order of the principal axis is given by a product of any number of different Pierpont primes (...,5,7,13,17,19,37,73,97,109,163,...) times arbitrary powers of two and three. While some characters of this group can be expressed using real integers and square roots alone, others need complex numbers and third roots. κ The regular nonagon or enneagon is not constructible by ruler and compass because cos(2*π/9) has an algebraic degree of 3. (It can be constructed by extended methods that allow angle trisection, as this corresponds to solving cubic equations). The value of cos(2*π/9) can be expressed using cubic roots and complex numbers, which, however, is not very useful for a real-valued quantity: 2*cos(2π/9) = (3√−4+i*4*√3 + 3√−4−i*4*√3)/2. Therefore, regular polygons of order 18,27,36,45,54 etc. are also inconstructible, and their cosines have no representation in real radicals.
| D16d | ||
| D17d | ||
| C18 C18v C18h D18 D18h | D18d | S18 |
| D19d | ||
| D20d |
This Character Table for the D18d point group was created by Gernot Katzer.
For other groups and some explanations, see the Main Page.