S. No Symmetry Species Cs Observed Frequency(cm-1) Methods Vibrational  Assignments FT-IR FT-Raman HF B3LYP B3PW91 6-311+G (d, p) 6-311+G (d, p) 6-311++G (d, p) 6-311+G (d, p) 6-311++G (d, p) 1 A′ 3090w -     3093 3097 3095 3090 3096 (C-H) υ 2 A′ 3080m - 3080 3084 3082 3079 3083 (C-H) υ 3 A′ - 3070m 3071 3076 3073 3070 3075 (C-H) υ 4 A′ - 3060m 3059 3063 3060 3057 3062 (C-H) υ 5 A′ - 3040s 3056 3062 3059 3056 3060 (C-H) υ 6 A′ 3030s - 2976 2997 2994 2998 3006 (C-H) υ 7 A′ - 3010w 2973 2994 2991 2993 3001 (C-H) υ 8 A′ 3005w 3005w 2956 2972 2970 2973 2979 (C-H) υ 9 A′ 2960s   2937 2951 2949 2954 2958 (C-H) υ 10 A′   2940s 2927 2937 2935 2935 2938 (C-H) υ 11 A′ 2930s - 2920 2931 2930 2930 2931 (C-H) υ 12 A′ - 2870m 2912 2928 2925 2927 2929 (C-H) υ 13 A′ 1610w - 1653 1596 1596 1621 1605 (C=C) υ 14 A′ 1605w 1605m 1628 1578 1575 1599 1584 (C=C) υ 15 A′ 1590w 1590m 1524 1513 1558 1490 1478 (C=C) υ 16 A″ 1500s - 1505 1499 1503 1461 1454 (CH3) α 17 A′ 1495s - 1491 1486 1490 1448 1443 (C-C) υ 18 A′ 1455m - 1442 1484 1442 1440 1436 (C-C) υ 19 A′ 1450s - 1436 1476 1434 1438 1430 (C-C) υ 20 A′ - 1440w 1428 1421 1429 1433 1428 (C-C) υ 21 A′ 1380w - 1374 1353 1361 1363 1354 (C-C) υ 22 A′ 1340w 1340w 1352 1325 1333 1323 1330 (C-C) υ 23 A′ - 1290w 1315 1305 1312 1293 1316 (C-H)  δ 24 A′ - 1280w 1277 1286 1294 1267 1306 (C-H)  δ 25 A′ - 1250w 1272 1267 1275 1253 1273 (C-H)  δ 26 A′ - 1200s 1221 1262 1203 1253 1262 (C-H)  δ 27 A′ - 1190w 1181 1196 1193 1186 1201 (C-H)  δ 28 A′ - 1180w 1170 1175 1172 1174 1188 (C-H)  δ 29 A′ 1160w 1160w 1150 1152 1149 1142 1157 (C-H)  δ 30 A′ 1105w - 1100 1132 1129 1117 1137 (C-H)  δ 31 A′ 1100w - 1106 1094 1075 1100 1069 (C-H)  δ 32 A′ 1095w 1095w 1077 1078 1059 1094 1057 (C-H)  δ 33 A′ 1050w - 1051 1041 1023 1051 1019 (C-H)  δ 34 A′ 1040w - 1032 1022 1004 1036 1007 (C-H)  δ 35 A′ 1030w - 1024 1010 993 1032 1002 (C-C)  δ 36 A′ - 1000s 1018 990 972 1001 968 (C-C)  δ 37 A′ 910w   943 974 952 997 913 (C-C)  δ 38 A″ 895w - 929 956 937 979 902 (C-H) γ 39 A″ 890w 890w 882 868 886 895 896 (C-H) γ  40 A″ - 865w 824 835 855 839 871 (C-H) γ 41 A″ - 840w 814 821 841 815 846 (C-H) γ 42 A″ 820w 820 806 798 815 802 826 (C-H) γ 43 A″ 740vs 740vs 757 770 788 771 760 (C-H) γ 44 A″ 705vs - 710 711 727 714 700 (C-H) γ  45 A″ 700vs - 682 697 713 691 682 (C-H) γ 46 A″ - 610m 664 665 649 666 655 (C-H) γ 47 A″ 590s 590w 583 594 580 591 581 (C-H) γ  48 A″ 570vs   550 559 546 558 547 (C-H) γ 49 A″ 530vw   505 493 542 496 489 (C-H) γ 50 A′ 490s - 418 410 442 404 398 (CCC) δ 51 A′ 480s - 341 343 370 337 332 (CCC) δ 52 A′ 470vw - 305 307 330 302 299 (CCC) δ 53 A″ 400 m - 278 276 297 271 266 (CCC)  γ 54 A″ 370m   238 227 245 225 222 (CCC)  γ 55 A″ 280s - 103 101 109 99 98 (CCC)  γ 56 A″ 270s - 84 82 89 82 80 (C-C)  γ 57 A″ 260s _- 37 45 48 38 43 (C-C)  γ

Table 2: Observed and calculated vibrational frequencies of propylbenzene using HF and DFT (B3LYP & B3PW91) at the 6-31+& 6-311+G (d, p) level.