Table 7: Frequenciesa (in cm−1) and IR intensities (in km/mol) of various vibrational modesb obtained from the theoretical vibrational spectra of the dipeptides in gas and aqueous phases. Intensities are given in brackets.

DipeptidesPhases  (C4=O11)  (N6–H10)  (C4–N6)  (N5–H)  (N5–H)Sis (N5–H)  (C7–H)  (C3–H)

Sec-ValAqueous1699 (573)3433 (160)1552 (673)3384 (9)3464 (12)1667 (59)2977 (6)2941 (6)
Gas1749 (273)3469 (57)1554 (406)3382 (2)3463 (7)1675 (43)2968 (10)2937 (2)
Sec-LeuAqueous1696 (533)3442 (155)1550 (555)3383 (8)3464 (11)1670 (61)2975 (9)2942 (7)
Gas1747 (266)3458 (66)1559 (359)3382 (3)3465 (3)1676 (44)2962 (7)2939 (2)
Sec-AspAqueous1706 (623)3415 (169)1554 (597)3383 (11)3464 (13)1667 (56)2972 (16)2941 (6)
Gas1758 (260)3429 (80)1553 (268)3376 (9)3467 (6)1675 (58)2951 (24)2938 (3)
Sec-SerAqueous1704 (533)3420 (179)1550 (555)3381 (12)3463 (14)1668 (58)3027 (8)2942 (6)
Gas1754 (275)3454 (76)1548 (380)3382 (3)3464 (3)1676 (41)3028 (3)2940 (2)
Sec-GlnAqueous1697 (628)3440 (162)1548 (583)3381 (9)3461 (12)1668 (55)2970 (21)2940 (6)
Gas1748 (277)3457 (73)1551 (447)3383 (3)3466 (4)1676 (42)2978 (4)2939 (2)
Sec-HisAqueous1704 (507)3416 (175)1546 (621)3384 (12)3465 (13)1669 (58)3027 (8)2940 (6)
Gas1754 (239)3450 (77)1548 (413)3382 (3)3464 (3)1676 (43)3021 (5)2940 (2)
Sec-PylAqueous1698 (537)3430 (161)1556 (609)3384 (10)3464 (12)1667 (62)2976 (4)2940 (6)
Gas1747 (264)3458 (73)1560 (380)3382 (3)3465 (3)1676 (41)2988 (17)2938 (2)

The frequencies below 1800 cm−1 are scaled with 1.01 and for those above 1800 cm−1 a correction factor 0.9679 is used.
bVibrational modes: ν: stretching; Sis: scissoring; s: symmetric; as: asymmetric.