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Supporting Information

Infrared Detection of the 1,3-Dimethyl Cyclopentadienyl Cation, an Isomer of Protonated Toluene

Jonathan D. Mosley, Justin W. Young, Michael A. Duncan*

Department of Chemistry, University of Georgia, Athens, GA 30602, U.S.A.*Corresponding author: maduncan@uga.edu

*Phone: +1-706-542-1998

Table S1. Selected isomers of C7H11+ calculated at the B3LYP level of theory using GAMESS-

US. Relative energies (∆E) are zero-point vibrational energy corrected.

Isomer B3LYP/6-311+G(d,p) Energy (Hartrees) ∆E (kcal/mol)para-protonated toluene (1) -271.772576 0.0ortho-protonated toluene (2) -271.770530 +1.4meta-protonated toluene (3) -271.764490 +5.26-methyl fulvenium (4) -271.758214 +9.0ipso-protonated toluene (4') -271.758122 +10.01,3-protonated cycloheptatriene (5) -271.734230 +25.31,2-protonated cycloheptatriene (6) -271.740620 +21.33-notricyclyl (7) -271.710390 +40.71,4-protonated cycloheptatriene (8) -271.722055 +32.01,3-dimethylcyclopentadienyl (9) -271.725661 +27.51,2-dimethylcyclopentadienyl (10) -271.713529 +34.9

Figure S1. The optimized geometry of 1 (Cs symmetry) calculated at the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 1 calculatedat the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms.

78.9 (1.1), 139.1 (6.2), 275.2 (1.7), 339.8 (0.1), 357.0 (0.1), 506.0 (1.6), 530.6 (24.5), 598.9 (6.4), 727.0 (18.4), 782.3 (0.6), 798.9 (0.0), 878.7 (14.3), 900.5 (22.0), 979.5 (11.6), 995.2 (9.1), 1009.9 (0.1), 1032.8 (40.7), 1039.6 (3.1), 1046.1 (0.8), 1158.1 (0.0), 1169.1 (0.7), 1207.6 (53.2), 1245.4 (0.5), 1306.1 (116.7), 1337.0 (28.3), 1386.8 (68.9), 1392.7 (2.0), 1442.1 (34.8), 1481.8 (46.0), 1489.2 (9.5), 1496.7 (109.6), 1537.6 (27.7), 1648.9 (184.8), 2954.7 (30.7), 2959.2 (31.1), 2992.8 (33.7), 3081.5 (2.8), 3134.0 (0.3), 3179.5 (1.1), 3179.7 (2.3), 3193.2 (1.7), 3194.9 (1.0)

Figure S2. The optimized geometry of 2 calculated at the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 2 calculatedat the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms.

83.6 (2.7), 143.5 (3.9), 239.1 (9.4), 347.1 (0.2), 422.3 (3.4), 436.9 (9.0), 505.4 (4.6), 606.4 (1.9), 709.9 (35.2), 767.6 (2.7), 840.5 (18.4), 885.6 (4.3), 919.8 (4.8), 988.9 (12.9), 1008.2 (3.5), 1011.8 (0.8), 1043.6 (13.8), 1057.6 (0.6), 1060.8 (0.6), 1173.2 (6.5), 1190.2 (3.9), 1201.8 (20.0), 1214.6 (8.7), 1304.3 (85.6), 1332.3 (33.8), 1396.8 (48.4), 1408.5 (2.3), 1439.3 (1.8), 1467.8 (45.3), 1474.2 (118.4), 1502.8 (214.0), 1558.5 (3.8), 1643.9 (97.6), 2954.7 (33.2), 2981.0 (18.8), 3009.7 (16.1), 3077.3 (1.4), 3133.9 (2.9), 3173.7 (0.1), 3183.6 (3.9), 3192.6 (1.9), 3206.6 (1.6)

Figure S3. The optimized geometry of 3 calculated at the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 3 calculatedat the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms.

66.8 (0.6), 188.9 (0.4), 225.3 (14.9), 342.5 (0.2), 373.2 (4.6), 458.7 (4.1), 505.1 (3.4), 607.7 (1.0), 680.6 (44.8), 772.9 (4.8), 816.4 (1.4), 893.1 (12.8), 933.7 (9.3), 995.2 (2.3), 999.0 (8.0), 1029.8 (0.4), 1046.4 (6.8), 1068.7 (30.3), 1079.6 (3.7), 1145.6 (0.8), 1152.4 (0.1), 1195.0 (23.7), 1220.8 (4.2), 1286.1 (110.2), 1345.6 (1.2), 1389.1 (31.6), 1429.8 (22.1), 1438.4 (34.7), 1481.9 (16.4), 1483.4 (86.7), 1498.0 (77.4), 1586.7 (27.2), 1633.6 (41.5), 2943.8 (17.6), 2948.4 (54.7), 3038.7 (1.4), 3095.1 (0.7), 3130.7 (2.6), 3162.5 (0.8), 3176.6 (0.8), 3186.3 (4.6), 3203.7 (2.7)

Figure S4. The optimized geometry of 4' (Cs symmetry) calculated at the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 4' calculatedat the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms.

90.5 (2.1), 244.3 (0.7), 282.3 (0.1), 372.1 (0.3), 383.0 (0.0), 516.8 (7.0), 596.3 (4.2), 618.0 (20.3), 743.6 (37.9), 812.6 (35.5), 822.8 (3.2), 932.6 (17.1), 959.0 (3.9), 973.9 (16.1), 1014.9 (2.0), 1019.3 (1.3), 1047.9 (6.8), 1052.8 (10.8), 1062.8 (1.8), 1096.8 (8.0), 1139.8 (0.0), 1145.1 (38.7), 1203.1 (12.4), 1217.8 (5.3), 1340.4 (11.2), 1405.4 (0.1), 1409.9 (9.1), 1480.2 (35.6), 1481.0 (141.7), 1495.2 (7.2), 1502.2 (14.3), 1570.8 (0.3), 1633.5 (109.0), 2867.8 (47.8), 3055.8 (5.6), 3141.6 (0.5), 3142.4 (2.5), 3175.3 (0.5), 3176.9 (1.0), 3180.6 (4.2), 3201.5 (3.2), 3204.1 (2.8)

Figure S5. The optimized geometry of 4 (Cs symmetry) calculated at the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 4 calculatedat the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms.

3.4 (0.16), 3.3 (0.02), 1.5 (0.16), 0.3 (0.02), 0.1 (0.12), 0.6 (0.09), 131.0 (1.50), 175.5 (1.38), 198.3 (0.55), 262.5 (1.79), 394.6 (11.26), 467.4 (0.37), 486.3 (12.15), 643.7 (0.19), 749.9 (28.41), 821.2 (25.69), 847.6 (0.03), 877.9 (36.47), 911.9 (20.16) 965.9 (33.30), 978.4 (14.84), 982.6 (3.39), 1020.9 (0.33), 1062.3 (0.06), 1086.0 (61.71), 1130.4 (2.83), 1146.6 (0.48), 1148.8 (0.04), 1255.4 (10.33), 1276.8 (37.80), 1372.4 (36.93), 1380.5 (53.46), 1383.2 (93.44), 1413.8 (44.75), 1452.9 (51.95), 1453.2 (15.05), 1470.6 (237.37), 1527.7 (50.21), 1646.6 (300.03), 3003.6 (39.45), 3015.4 (14.19), 3037.8 (3.06), 3039.6 (3.57), 3130.6 (6.56), 3148.3 (9.23), 3199.0 (0.97), 3206.9 (5.83), 3234.4 (7.95)

Figure S6. The optimized geometry of 5 calculated at the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 5 calculatedat the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms.

219.8 (6.0), 235.9 (6.5), 361.8 (4.8), 395.3 (12.2), 488.8 (3.3), 522.2 (8.6), 621.0 (10.8), 721.2 (95.1), 750.3 (52.7), 802.4 (16.5), 869.7 (2.9), 898.0 (7.5), 931.6 (8.7), 965.5 (70.8), 982.2 (11.6), 1027.5 (28.7), 1053.4 (9.7), 1061.5 (1.9), 1075.3 (5.3), 1112.8 (13.4), 1123.7 (1.5), 1194.4 (15.1), 1199.5 (30.2), 1208.1 (11.9), 1256.7 (6.0), 1367.4 (2.2), 1386.8 (34.9), 1412.5 (38.7), 1431.5 (13.2), 1451.1 (23.1), 1491.9 (40.1), 1540.4 (77.5), 1604.1 (57.6), 2998.9 (9.4), 3016.6 (2.5), 3127.9 (1.7), 3153.8 (1.5), 3172.8 (1.6), 3176.1 (5.3), 3193.5 (5.9), 3205.5 (0.5), 3226.9 (7.4)

Figure S7. The optimized geometry of 6 (C2 symmetry) calculated at the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 6 calculatedat the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms.

100.4 (7.6), 160.9 (0.5), 347.9 (2.1), 365.5 (0.6), 410.5 (0.3), 433.9 (20.0), 591.8 (22.0), 749.3 (47.8), 763.6 (0.7), 793.5 (4.3), 882.9 (1.4), 910.5 (11.9), 927.5 (2.3), 938.8 (0.4), 989.7 (19.4), 991.4 (0.6), 1063.6 (9.8), 1082.2 (0.1), 1100.1 (1.7), 1171.2 (10.9), 1207.0 (9.7), 1271.6 (33.2), 1286.1 (3.2), 1293.5 (48.3), 1380.4 (7.9), 1397.2 (19.8), 1430.8 (41.1), 1433.0 (37.4), 1456.6 (19.6), 1487.0 (3.0), 1532.9 (358.8), 1574.6 (1.8), 1639.0 (107.0), 2947.4 (3.8), 2956.0 (0.3), 3073.7 (0.2), 3076.6 (0.4), 3147.1 (0.0), 3152.2 (1.3), 3153.5 (2.2), 3182.1 (1.1), 3184.5 (1.2)

Figure S8. The optimized geometry of 7 (Cs symmetry) calculated at the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 7 calculatedat the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms.

47.3 (0.7), 414.2 (2.3), 432.5 (1.1), 479.8 (0.5), 546.4 (61.2), 706.0 (10.0), 766.8 (1.9), 812.3 (3.1), 823.8 (34.2), 851.3 (13.5), 878.7 (0.8), 893.0 (0.4), 934.4 (11.5), 943.4 (0.3), 987.2 (2.0), 994.0 (0.5), 1046.2 (3.0), 1049.0 (4.2), 1072.3 (0.1), 1096.7 (10.7), 1106.3 (5.9), 1160.8 (1.0), 1161.2 (12.6), 1218.8 (0.2), 1258.8 (8.1), 1277.1 (3.7), 1295.7 (0.3), 1331.7 (33.0), 1345.8 (20.5), 1436.7 (6.8), 1501.8 (11.7), 1516.4 (6.6), 1534.0 (36.1), 3067.1 (0.6), 3070.8 (6.2), 3128.2 (0.0), 3129.7 (0.3), 3169.8 (0.5), 3190.7 (8.8), 3193.4 (4.7), 3203.1 (8.7), 3253.0 (25.5)

Figure S9. The optimized geometry of 8 calculated at the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 8 calculatedat the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms.

152.0 (37.7), 166.1 (4.0), 303.8 (18.0), 358.3 (1.6), 392.5 (25.7), 459.3 (7.5), 641.0 (39.9), 664.7 (10.7), 725.6 (45.8), 812.5 (11.3), 848.6 (58.7), 878.9 (12.2), 917.4 (2.4), 931.3 (10.5), 947.1 (25.0), 1009.1 (5.2), 1027.6 (9.0), 1047.7 (1.2), 1060.4 (5.1), 1125.7 (2.1), 1183.1 (9.7), 1195.1 (6.1), 1240.0 (2.4), 1250.1 (23.4), 1257.8 (8.7), 1355.6 (51.7), 1365.8 (12.8), 1399.8 (3.2), 1425.3 (8.5), 1499.1 (16.4), 1517.6 (4.6), 1576.7 (110.9), 1644.6 (26.2), 2885.5 (28.5), 3059.7 (2.7), 3066.1 (2.1), 3140.6 (0.8), 3146.9 (4.9), 3159.2 (1.9), 3165.4 (5.1), 3170.1 (5.0), 3192.6 (4.3)

Figure S10. The optimized geometry of 9 (C2v symmetry) calculated at the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 9 calculatedat the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms.

102.4 (5.6), 156.9 (0.0), 173.3 (4.4), 250.0 (0.1), 271.8 (0.8), 391.2 (1.8), 517.4 (50.0), 539.8 (13.4), 569.6 (0.9), 581.7 (0.0), 737.9 (28.6), 809.2 (14.4), 877.8 (44.5), 891.7 (1.2), 932.8 (10.9), 957.7 (0.4), 980.0 (0.6), 988.6 (45.6), 1011.6 (0.0), 1100.7 (70.6), 1114.0 (4.8), 1191.2 (156.5), 1296.2 (1.3), 1309.9 (9.8), 1343.9 (133.1), 1378.2 (1.9), 1422.3 (31.2), 1425.2 (0.0), 1428.3 (31.5), 1436.3 (327.1), 1521.8 (379.5), 1530.2 (0.0), 1670.7 (10.9), 2971.4 (220.7), 2975.8 (4.3), 2998.8 (8.4), 2999.1 (0.0), 3150.0 (17.1), 3150.3 (0.5), 3223.2 (4.2), 3238.1 (14.6), 3244.0 (4.4)

Figure S11. The optimized geometry of 10 calculated at the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 10 calculatedat the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C and H atoms.

74.5 (0.0), 152.9 (0.0), 157.3 (6.0), 225.8 (13.7), 248.0 (0.0), 389.3 (3.6), 413.5 (184.7), 418.4 (0.1), 571.1 (0.0), 655.2 (0.1), 803.7 (2.2), 809.3 (39.1), 827.9 (0.0), 924.8 (397.3), 971.7 (31.9), 982.5 (14.3), 985.8 (27.1), 1013.4 (0.0), 1043.0 (9.0), 1048.0 (0.7), 1097.3 (1.5), 1253.6 (8.9), 1272.5 (0.0), 1327.4 (12.3), 1342.2 (105.0), 1364.3 (27.8), 1379.1 (141.2), 1428.1 (0.0), 1428.5 (41.2), 1454.5 (46.6), 1467.6 (61.7), 1598.3 (65.7), 1616.6 (232.6), 2971.0 (32.3), 2983.3 (40.4), 3000.7 (0.0), 3014.8 (2.6), 3155.7 (1.9), 3156.4 (3.1), 3189.5 (0.5), 3212.0 (10.7), 3216.3 (7.6)

Figure S12. Experiment compared to theory for 1,3-dimethyl cyclopentenyl cation. Predicted vibrations were computed at the B3LYP/6-311+G(d,p) level of theory using GAMESS-US. A 0.981 scale factor was used in the fingerprint region and a 0.966 scale factor was used in the C−H stretching region.

Figure S13. The optimized geometry of 1 (Cs symmetry) calculated at the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 1 calculatedat the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms.

25.9 (4.1), 139.4 (7.2), 232.1 (2.7), 323.7 (0.4), 351.0 (0.0), 500.1 (0.1), 510.0 (17.5), 588.0 (5.5), 702.8 (12.1), 780.4 (0.2), 783.6 (2.2), 860.4 (21.5), 910.0 (30.0), 976.2 (10.1), 982.9 (0.8), 996.8 (1.7), 1009.4 (0.8), 1032.0 (10.5), 1034.4 (7.1), 1134.7 (1.2), 1148.5 (0.7), 1204.3 (31.1), 1249.9 (10.0), 1274.7 (117.6), 1325.3 (14.0), 1370.4 (29.9), 1402.4 (5.8), 1455.5 (11.3), 1462.6 (25.1), 1481.2 (31.9), 1544.2 (9.7), 1574.4 (150.8), 1654.2 (156.1), 2986.3 (77.0), 3010.8 (21.3), 3051.3 (27.7), 3126.7 (3.7), 3199.6 (9.9), 3221.3 (1.2), 3222.3 (2.6), 3236.9 (3.5), 3241.8 (2.2),

Figure S14. The optimized geometry of 2 calculated at the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 2 calculatedat the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms.

74.6 (1.3), 118.0 (9.9), 211.6 (8.0), 340.8 (0.3), 384.8 (0.9), 413.6 (9.7), 497.6 (3.6), 594.2 (1.6), 683.7 (24.8), 770.6 (2.9), 809.8 (19.1), 873.2 (5.8), 916.9 (8.3), 978.1 (6.0), 989.6 (14.9), 1002.1 (2.7), 1010.7 (3.9), 1035.8 (2.6), 1059.3 (1.2), 1128.7 (3.1), 1175.9 (6.0), 1198.1 (12.2), 1225.4 (6.8), 1262.9 (84.5), 1315.1 (13.2), 1387.0 (22.4), 1423.5 (1.4), 1434.3 (13.7), 1466.1 (15.7), 1469.5 (32.4), 1544.5 (147.0), 1593.6 (166.4), 1654.1 (102.5), 2949.1 (42.6), 3045.7 (15.1), 3052.2 (14.9), 3137.2 (3.4), 3190.1 (1.7), 3214.0 (0.5), 3226.2 (3.5), 3238.0 (2.3), 3255.0 (2.6)

Figure S15. The optimized geometry of 3 calculated at the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 3 calculatedat the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms.

95.4 (0.1), 130.9 (23.6), 188.7 (1.5), 330.4 (0.3), 347.5 (4.0), 430.9 (4.3), 494.5 (1.6), 592.9 (1.4), 655.3 (33.5), 769.6 (6.6), 784.2 (8.3), 854.8 (11.0), 944.1 (14.3), 972.8 (5.2), 990.8 (11.4), 991.5 (2.1), 1026.4 (1.7), 1057.1 (21.3), 1058.8 (2.4), 1112.6 (0.9), 1138.1 (0.9), 1190.7 (22.2), 1228.2 (57.7), 1245.3 (39.0), 1327.8 (3.5), 1386.7 (25.8), 1409.8 (5.3), 1447.5 (8.5), 1473.1 (4.0), 1480.8 (16.9), 1564.0 (194.3), 1608.6 (41.0), 1638.3 (20.9), 2970.2 (86.4), 2990.3 (16.4), 3076.1 (0.7), 3167.1 (0.2), 3190.8 (1.6), 3197.9 (1.4), 3214.2 (4.2), 3228.7 (6.0), 3250.9 (1.6)

Figure S16. The optimized geometry of 4' (Cs symmetry) calculated at the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 4' calculatedat the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms.

60.5 (3.2), 227.5 (0.2), 276.2 (0.2), 349.5 (0.3), 378.9 (0.1), 524.7 (10.9), 576.9 (3.3), 601.7 (7.1), 743.2 (96.6), 824.1 (0.9), 832.6 (4.3), 873.8 (127.5), 955.9 (12.0), 967.8 (5.9), 995.3 (0.1), 996.8 (0.3), 1016.2 (0.3), 1025.2 (0.4), 1036.8 (2.2), 1076.8 (2.7), 1132.7 (31.6), 1155.4 (0.7), 1196.4 (6.8), 1203.4 (0.0), 1340.5 (3.8), 1366.1 (2.3), 1422.7 (7.1), 1462.0 (13.9), 1481.6 (12.0), 1481.9 (26.7), 1545.2 (92.1), 1598.4 (68.6), 1639.5 (68.8), 3038.9 (24.1), 3085.6 (2.5), 3203.8 (1.2), 3206.8 (0.2), 3213.9 (0.2), 3215.3 (2.9), 3219.1 (1.5), 3250.3 (2.8), 3251.9 (3.5)

Figure S17. The optimized geometry of 4 (Cs symmetry) calculated at the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 4 calculatedat the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms.

1.3 (0.12), 0.8 (0.18), 0.1 (0.13), 2.5 (0.08), 3.7 (0.15), 5.6 (0.96), 119.5 (1.72), 165.2 (0.29), 195.0 (0.08), 254.1 (1.86), 379.0 (13.38), 462.9 (0.35), 475.2 (11.59), 639.9 (1.44), 731.6 (23.98), 807.6 (28.18), 834.0 (1.40), 883.41 (35.10), 893.55 (17.80), 962.16 (7.12), 971.26 (38.74), 974.3 (9.85), 986.2 (1.63), 1046.1 (0.30), 1086.2 (58.64), 1122.6 (1.38), 1134.3 (0.94), 1158.0 (0.14), 1243.1 (5.47), 1266.6 (27.72), 1362.7 (22.26), 1366.1 (32.63), 1374.7 (45.17), 1426.5 (19.30), 1445.5 (14.38), 1451.6 (38.19), 1496.2 (110.01), 1529.7 (124.80), 1682.8 (359.03), 3046.1 (27.38), 3049.0 (17.70), 3099.4 (8.26), 3116.6 (2.81), 3180.7 (0.85), 3197.6 (7.75), 3233.5 (1.03), 3244.8 (7.38), 3277.6 (11.75)

Figure S18. The optimized geometry of 5 calculated at the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 5 calculatedat the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms.

211.3 (9.8), 231.0 (2.5), 357.8 (7.2), 377.0 (13.0), 455.6 (18.3), 487.5 (4.8), 604.1 (13.6), 716.0 (87.6), 781.7 (29.2), 793.2 (18.6), 859.9 (7.7), 896.5 (11.1), 916.9 (4.7), 969.0 (3.3), 979.7 (14.9), 997.8 (41.2), 1034.4 (10.0), 1053.8 (1.7), 1063.2 (0.8), 1098.3 (16.7), 1106.7 (7.0), 1175.8 (8.9), 1188.9 (9.1), 1198.2 (14.5), 1251.6 (7.6), 1340.0 (0.6), 1372.5 (23.2), 1395.3 (31.1), 1420.0 (6.9), 1441.0 (18.9), 1497.4 (13.4), 1586.6 (98.6), 1617.0 (27.6), 3037.5 (14.2), 3092.7 (3.4), 3153.1 (2.5), 3195.8 (0.6), 3218.7 (7.1), 3219.8 (4.8), 3239.5 (4.6), 3255.0 (6.1), 3275.3 (11.7)

Figure S19. The optimized geometry of 6 (C2 symmetry) calculated at the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 6 calculatedat the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms.

86.9 (12.7), 182.9 (0.1), 326.9 (3.6), 357.1 (0.2), 393.5 (0.6), 411.5 (16.9), 577.3 (15.1), 740.8 (45.9), 752.9 (0.0), 814.7 (3.3), 863.4 (1.7), 904.3 (8.3), 947.2 (9.0), 952.4 (1.4), 977.9 (21.0), 988.9 (1.0), 1033.6 (10.8), 1059.2 (0.9), 1114.6 (0.8), 1152.6 (5.4), 1200.9 (5.5), 1253.6 (11.4), 1262.3 (8.2), 1274.4 (32.9), 1364.8 (6.0), 1369.4 (12.5), 1418.9 (18.0), 1423.4 (26.9), 1431.1 (12.2), 1469.9 (1.2), 1565.6 (38.6), 1624.1 (385.2), 1650.4 (68.1), 2986.7 (4.2), 2994.6 (0.6), 3138.3 (0.5), 3141.8 (0.0), 3188.8 (0.0), 3196.1 (1.4), 3197.2 (5.5), 3235.2 (2.4), 3236.6 (2.8)

Figure S20. The optimized geometry of 7 calculated at the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 7 calculatedat the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms.

109.7 (31.6), 403.2 (4.7), 420.6 (1.7), 460.8 (12.4), 600.0 (25.6), 713.8 (14.7), 763.2 (1.8), 812.3 (6.9), 820.7 (37.4), 858.7 (8.2), 899.5 (1.1), 908.6 (3.2), 929.7 (5.1), 937.4 (4.9), 982.8 (0.9), 993.5 (0.1), 1019.9 (2.5), 1033.1 (1.6), 1057.1 (0.8), 1095.6 (8.2), 1096.6 (1.1), 1144.6 (2.7), 1145.8 (13.3), 1203.0 (0.7), 1250.0 (7.9), 1259.2 (0.2), 1268.1 (1.4), 1317.9 (35.1), 1337.7 (16.0), 1431.6 (4.6), 1476.0 (9.6), 1494.6 (5.5), 1560.8 (24.9), 3095.0 (1.0), 3103.4 (2.2), 3182.4 (1.1), 3183.5 (0.3), 3209.7 (1.0), 3232.8 (6.8), 3234.0 (11.6), 3243.5 (14.5), 3296.5 (20.7)

Figure S21. The optimized geometry of 8 calculated at the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 8 calculatedat the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms.

193.3 (1.2), 264.5 (32.0), 287.5 (9.1), 310.9 (16.2), 452.7 (7.7), 466.9 (8.7), 635.9 (10.6), 658.5 (31.0), 710.1 (22.7), 785.8 (52.4), 839.8 (40.1), 870.4 (7.9), 892.6 (6.6), 945.4 (1.6), 948.1 (3.3), 994.1 (8.4), 1007.6 (3.2), 1051.9 (6.8), 1057.4 (8.5), 1108.3 (0.7), 1115.4 (2.2), 1127.6 (8.2), 1187.3 (1.3), 1210.1 (5.9), 1237.5 (1.3), 1339.8 (0.3), 1363.4 (5.0), 1387.0 (44.3), 1405.9 (4.5), 1440.0 (22.3), 1499.8 (5.6), 1599.5 (24.9), 1640.6 (17.3), 2963.0 (28.4), 3139.8 (1.1), 3160.9 (4.6), 3201.0 (1.9), 3204.1 (7.0), 3209.6 (15.0), 3239.8 (3.7), 3247.4 (5.5), 3270.7 (7.8)

Figure S22. The optimized geometry of 9 (C2v symmetry) calculated at the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 9 calculatedat the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms.

88.3 (4.0), 145.3 (0.0), 160.2 (5.1), 243.0 (0.0), 262.7 (0.7), 377.3 (1.8), 518.7 (7.5), 524.9 (69.8), 563.9 (0.2), 570.7 (0.0), 709.4 (16.4), 807.7 (16.8), 871.4 (43.7), 901.5 (2.0), 903.5 (0.0), 969.6 (0.8), 971.3 (0.9), 979.0 (29.2), 1006.8 (0.0), 1100.0 (2.9), 1115.7 (123.7), 1181.1 (137.2), 1275.8 (3.8), 1305.7 (14.2), 1335.6 (85.8), 1387.1 (0.7), 1421.1 (20.8), 1427.1 (27.7), 1429.0 (213.3), 1430.2 (0.0), 1535.4 (0.2), 1561.1 (703.5), 1629.5 (13.4), 3015.3 (138.4), 3018.0 (1.3), 3077.6 (16.2), 3078.0 (0.0), 3209.8 (19.7), 3210.1 (0.0), 3262.0 (3.3), 3282.4 (23.6), 3284.8 (0.0)

Figure S23. The optimized geometry of 10 (C2v symmetry) calculated at the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms. Bond lengths (black) are in Angstroms. Bond angles (red) are in degrees.

The normal mode frequencies (unscaled) and intensities (km/mol) of 10 calculatedat the MP2(fc) level of theory using GAMESS-US. The aug-cc-pVDZ basis set was used for C and H atoms.

71.8 (0.1), 168.4 (0.4), 177.0 (10.9), 212.1 (520.6), 220.6 (5.5), 248.2 (0.1), 386.8 (5.0), 394.1 (0.2), 564.5 (0.0), 663.4 (0.2), 792.3 (39.2), 795.0 (5.4), 799.3 (0.0), 864.5 (574.8), 964.4 (14.4), 971.8 (37.8), 992.2 (63.6), 1007.7 (0.4), 1043.0 (1.5), 1048.3 (4.9), 1097.9 (1.2), 1235.9 (17.1), 1287.5 (4.4), 1323.6 (22.2), 1326.5 (122.0), 1374.4 (31.6), 1382.0 (81.7), 1436.5 (0.7), 1443.3 (27.7), 1444.8 (67.1), 1459.8 (56.6), 1606.6 (112.5), 1633.6 (157.9), 3031.6 (17.5), 3039.9 (30.4), 3098.9 (0.4), 3110.7 (3.1), 3193.6 (2.6), 3194.9 (7.6), 3227.3 (1.3), 3288.2 (15.7), 3290.4 (6.9)

Table S2. Selected isomers of C7H11+Ar calculated at the B3LYP level of theory using

GAMESS-US. Relative energies (∆E) are zero-point vibrational energy corrected. Binding energies (B.E.) are not corrected for zero point vibrational energy or basis set superposition errors.

Isomer B3LYP/6-311+G(d,p) ∆E (kcal/mol) B.E. (cm-1)1-Ar -799.257628 0.0 1539-Ar -799.210672 27.3 144

Figure S24. The optimized geometry of 1−Ar calculated at the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C, H and Ar atoms. Bond lengths (black) are in Angstroms.

The normal mode frequencies (unscaled) and intensities (km/mol) of 1−Ar calculatedat the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C, H and Ar atoms.

7.7 (0.8), 8.4 (3.4), 16.0 (1.3), 115.6 (0.9), 142.9 (6.2), 275.8 (2.6), 339.6 (0.0), 356.4 (0.2), 505.9 (1.9), 532.7 (22.1), 598.9 (3.0), 728.1 (19.5), 782.7 (1.3), 798.5 (0.1), 878.4 (17.6), 900.6 (21.8), 979.9 (7.2), 995.0 (7.3), 1009.8 (0.1), 1034.6 (35.6), 1040.3 (0.7), 1045.4 (0.3), 1160.4 (0.0), 1169.4 (0.2), 1207.5 (47.2), 1245.3 (1.5), 1305.7 (131.2), 1338.8 (43.0), 1393.5 (42.0), 1395.0 (11.7), 1443.8 (31.3), 1481.5 (49.4), 1488.7 (12.8), 1497.0 (101.8), 1537.8 (36.2), 1648.8 (185.6), 2953.5 (32.9), 2961.6 (38.7), 2995.7 (35.6), 3082.1 (1.0), 3134.3 (0.3), 3179.3 (13.1), 3179.6 (12.9), 3192.9 (16.0), 3194.6 (3.2)

Figure S25. The optimized geometry of 9−Ar calculated at the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C, H and Ar atoms. Bond lengths (black) are in Angstroms.

The normal mode frequencies (unscaled) and intensities (km/mol) of 9−Ar calculatedat the B3LYP level of theory using GAMESS-US. The 6-311+G(d,p) basis set was used for C, H and Ar atoms.

-5.6 (5.1), -4.5 (0.4), 13.9 (4.8), 93.1 (7.1), 135.0 (0.0), 156.8 (16.2), 252.7 (0.0), 264.5 (0.2), 383.5 (1.1), 512.6 (47.7), 538.3 (18.2), 569.3 (0.2), 580.1 (0.0), 741.0 (29.7), 806.2 (15.2), 874.9 (45.7), 890.3 (1.1), 932.4 (12.8), 961.7 (0.0), 975.2 (0.5), 988.1 (54.3), 1010.4 (0.2), 1097.6 (70.8), 1113.6 (4.0), 1186.5 (154.3), 1294.9 (0.6), 1308.8 (17.3), 1343.3 (177.6), 1377.7 (0.8), 1420.7 (86.0), 1423.8 (0.3), 1426.6 (28.8), 1431.7 (325.4), 1518.9 (368.5), 1527.7 (0.3), 1667.7 (10.9), 2971.9 (175.5), 2976.2 (0.1), 2999.7 (12.7), 3000.0 (0.2), 3148.6 (14.4), 3149.0 (14.3), 3223.3 (1.7), 3237.3 (13.2), 3244.1 (3.4)