Table 1 Overview of relevant Raman modes found in amorphous silica.

430

δ_breath(Si–O–Si)

Symmetric breathing modes of ≥5-fold Si–O–Si rings^a

450–490

δ_rock(Si–O–Si)

Silica rocking bands^a

488–495

D₁

Defect band = symmetric breathing modes of planar fourfold Si–O–Si rings^ab

601

D₂

Defect band = symmetric breathing modes of planar threefold Si–O–Si rings^a

783–837

δ_bend(Si–O–Si)

Silica bending bands^a

860

ν_as(O₂Si=NBO₂)

Asymmetric stretching of Q^2a

967–970

ν_as(O₃Si–NBO)

Asymmetric stretching modes of Q³

ν_as(O₃Si–OH)

Asymmetric stretching of Si–O in surface silanol groups^c

1060–1170

ν_s(Si–O–Si))

Si–O–Si stretching modes^a

~1630

ν₂(H₂O)

Bending mode of ‘free’ water and water H-bonded to H⁺ of silanol group^c

3250

2ν₂(H₂O)

First overtone of water bending mode^d

3450

ν₁(H₂O)

Symmetric stretching mode of water^d

3520

Superimposition of OH vibrations of adsorbed water molecules and vicinal/geminal silanol groups^d

3610

ν₃(H₂O)

Asymmetric stretching mode of water^d

3615

ν_s(SiO–H)

Stretching mode of silanol groups (H-bonded to O of water)^c

~3680

ν_s(Si–OH)

Stretching mode of vicinal/geminal silanol groups^a

3750

ν_s(Si–OH)

Stretching mode of isolated silanol groups^a