Table 1: Observed and calculated wavenumbers (cm−1) and assignments for citric acid dimmer.

ExperimentalaMonomerbDimera
IRRamanIRRamanAssignmentSQMcAssignmenta

3535 vw 𝜈 O–H3537ν O33–H39
3535 vw 𝜈 O–H3527ν O3–H4
3498 s 𝜈 O–H3527ν O19–H21
3480 vw 𝜈 O–H3525ν O40–H42
3446 m3446 vw3482ν O13–H14
3350 sh3342 vw3470ν O31–H35
3291 s3276 vw3066O22–H24
3247 sh
3040 sh
3035 sh3012νa CH2 op
2994 w2996 w3000 𝜈 a CH23009νa CH2 op
2994 w2996 w3006νa CH2 ip
2994 w2996 w2975 𝜈 a CH23003νa CH2 ip
2982 m2952νs CH2 ip
2982 m2950 𝜈 s CH22951νs CH2 ip
2982 m2934 (21) 𝜈 s CH22946νs CH2 op
2950 w2961 w2945νs CH2 op
2933 w2929 m2942O10–H12
1756 vs1786νs C=O1
1745 sh1750 w1783νs C=O2
1735 s1775νa C=O2
1735 s1771νa C=O1
1708 vs1708 w1706 s1736 (10) 𝜈 C=O1726νa C=O3
1698 sh1693 vs1695 sh1693 (11) 𝜈 C=O1677νs C=O3
1493 vs1483δs COH
1469 w1463νa C–C2
1430 m1432 m, br1427 s1425 mδCH2,1447ν C29–C30
δCH3
1430 m1432 m, br1430δCH2 ip
1424 sh1426δCH2 ip
1420 sh1417δCH2 op
1413 w1412δCH2 op
1389 m1391 s1389 s1389 (9)δ COH,1402δa COH
wag CH3
1389 m1385wag CH2 op
1389 m1383δC8–O13–H14
1365 w1381wag CH2 ip
1358 w1350 w1350 wτCH21352ρCH2 ip
1340 sh1347 w1325 vwwag CH21334δs COH
1308 w1308δs COH
1308 w1306wag CH2 ip, δC38–O40–H42
1308 w1301 vw1303δa COH
1292 w1291 vw1303ρCH2 ip, wag CH2 ip
1285 vw1280 wδ COH,1289ρCH2 op
wag CH3
1256 vw1266νa C–O
1242 m1258νs C–O
1214 m1229 w1219ρCH2 ip
1214 m1211 m1210 w1205 sτCH21212ρCH2 op
1199 sh1201 w1195 w 𝜈 C–O
1174 s1179 w1175 sδ COH1169ν C30–O33
1167 w1155ν C18–O19
1140 s1141 s1141 (3) 𝜈 C–O1145ν C38–O40
1140 s1140 w1140ν C1–O3
1140 s1130 w1127ν C8–O13
1081 w1083 m1090 w1080 s 𝜈 C–C1112δa COH
1053 m1053 m1053 (6) 𝜈 C–C1059ν C8–C5, ν C8–C15
1051 w1057ν C29–C32, ν C29–C26
1036 sh1039wag CH2 op
1036 sh1036τwCH2 op
966 vw926νs C–C2
945 w943 vs943 m943 (20) 𝜈 C–O911νs C–C1
914 sh886τwCH2 op
904 w904 m885τwCH2 op
904 w904 m900 m 𝜈 C–C872ν C29–O31
881 w886 w871τwCH2 ip
867 vw865τ(O22–H24), τ(O10–H12)
850 vw857ν C32–C38
842 vw842νa C–C1
842 vw827γa (OH–O)#
807 vw800δCCC op
795 sh810 w792γCOO2
781 s784 vs786 (29) 𝜈 C–C783δCOO2
729 sh723 w735δCOO5
700 w685δCOO4
686 w687 (6) 𝛾 COO674γCOO5
666 vw672γCOO3
656 sh660 sh655γCOO2 , τ(O3–H4),
τwCH2 op
640 w642 w645 w645 wτ(OH) 637τ(O40–H42)
627 vw631τ(O3–H4)
627 vw625τ(O19–H21)
627 vw621δCOO3
599 s597 w598 s598 (5)τ(OH) 616τ(O40–H42), δCOO5,
δC31–C29–C30, ρCOO5
574 w574δCOO6
571 w566γCOO4
550 w559 m556 (7)τ(OH) 544ρCOO2
541 w537δCOO1
520 sh528 vw519γCOO6
514 w499γCOO3 , τwCH2 ip,
τ(O19–H21)
504 w509 sh503 w496γCOO1
492 vw490τ(O33–H39)
477 sh476 vw485γCOO6
438 vvw453 w412ρCOO4
415 w420 wδCOO398τ(O31–H35)
397 w392 s383 (11)τ(OH) 390δC31–C29–C26
382 m387τ(O13–H14)
367 w373ρCOO3, ρCOO1
367 w358bδ COO368ρCOO5
348 w334bδ COO345ρCOO6
323 vw320bδ CCO329δC13–C8–C5
306 w294δC13–C8–C9
306 w271δC26–C29–C32
266 w251δC31–C29–C30
254 sh255bρCCC236δC5–C8–C15
247 vw245bδ CCC222δC9–C8–C5
237 vw223bδ CCC221δC31–C29–C32
217 w187bδ CCC180δC26–C29–C30
212 w174δCCC op
140b148νs(O–H–O)#
127τwCOO3
122δ(OH–O)#
118τwCOO5
105bδ CCC108νa(O–H–O)#, δCCC ip
99τwCOO5
88bτwCOO92δCCC ip
68bτwCOO72τwCC ip
57τCC2
53τwop#
44bτwCOO46τwCC op
39bτwCOO38τwCOO1
32τwCOO6
30τwCOO2
26τwCOO1, τwCOO2,
τwCOO3
25τCC1
11γs (OH–O)#
8τwCOO4

𝜈 : stretching; δ: scissoring; wag: wagging; 𝛾 : out-of plane deformation; ρ: rocking; τ: torsion, τw: twisting; a: antisymmetric; s: symmetric; s: strong; m: medium; w: weak; v: very; sh: shoulder; br: broad.
aThis work.
bCalculated by HF/4-21G method from [15].
cTheoretical values from SQM/B3LYP/6-31G* calculations for citric dimer acid.
# Intermonomer coordinates.