Question

please show how to use the character tables

Consider the three molecules, NF3, NF2l and NF12. (a) How many infrared active N-F stretching frequencies do you calculate for NF3? Why? (b) How many infrared active N-F stretching frequencies do you calculate for NFI? Why? (c) How many infrared active N-F stretching frequencies do you calculate for NFI2? Why? (d) Can Raman spectroscopy be used to identify each of these molecules? How?

Answer 1

Character table for C, point group linear, E] Oh Elon linear, rotations quadratic A 11 x,y, R, x, y2, 22, xy A" 1 - 1 2, Ry, Ry yz, xz

Character table for point group Czy is as following Csil E 20, 30 | A21 E 2 T 12 x2 + y2, 22 R (x, y)(R», R,) (x2 - y2, xy)(xz, yz) -1 0 2 - 1 0

=> FC NFZ, point group is, sv. The character table is attached N=4 , vibrational modes = 3N-6 F1 We get reducible representation on this, _ E 263 31v yed 1202 Now, reducing into the components, No. of AL = (12x12 + 271071) + 31270)3 = 3 no. of Az - <1 (1241) +210x1) + 3(27-00) = 1 no. of E.+ [6272) +2(04-1) + 31270) ) =4 a) BN = 3A, + A2 + 4E Non, From character table, we find, Framsorional - Aite rotational -625 Se, Tuib = r3n- traum - Tror = 2A1+2E Asow dimentioned the wodes ou 2 Liwerhore. IR as viels oro Roman active. , and NFI for both NFIz and NFI some same cone, the case, the point group is cs. Chanacter table is attached CSI E un - 3N | 12 | 92 No. of A's (1271 +271) = 7 no. of A" - (1271 +24-0 =5 trans 2A' +A" Trot - A'+2A" Cuib. = [3n - trom - Trot = 4A+2A". ab activa modes Here also all will be IR on well as famou achive