Question

Essay 2: List the different modes of dichloro methane. Which modes are IR active and which are Raman active? (20 points)

as detailed as possible with drawings please. thank you!

Answer 1

Answer: Dichiono methane (CH2012) cí o point group of chelin. a car ен. С12 Total number of vibrational mode = 3 n-6 = 15-6 = 9 na total number of atorns Total 9 different mode (viation) present in ch2012. The citeria fon te achve the made of vibration must "Change their dipole moment' during wibration. > Again the citeria fon Raman change their polarisatcility'. active , a molecule must The modes Quie giver be 1789,- 1. C-H Symmetric Strelching 0 IR Active Roman Active 2. C-H asymmetric stretching O 0 IP Acade - RAMAN ACTIVE 3. H-C-H in plane scissoring Coding) -> 10 Hitive . P.RAMAN CHive 4 H-C-H out of plane wogging (weding) AY -> le Active - OAMN ACTIVE 5. HAL-H out of plane twisting (berding) La → IR IMOCHve -> Roman ACH've 6. C-Cl symmetric stretching UK 200 -> IF Active → Raman AlHve

7. C-ci asymmetric Stretching Cur@ -> IR Achte my Raman active 8. H-c-H in plane Rocking (bending) @r) o~ -IR Active > Raman Active . a. ci-c-ci in plane scissoring (bending) IR Mchve - Raman Active Here in every mode (total of a) of vibration changes in polarisability occure during vibration so, all modes are Raman active. And every mode except Hocash out of plane twicting (bending) all other mode of vibration shows the change's their dipole moment during Nibration. so, the H-c-H out- of plane twisting is IR in active and other all mode are IR active as shown above structures.