Precise and accurate knowledge of the optical properties of amorphous silica is important because of the increasing application of SiO2 in optical and electrooptical devices, including photolithography masks for semiconductor fabrication, recently as a potential 157 nm mask substrate. The optical properties in the vacuum ultraviolet (VUV) region have been investigated, because they convey detailed information on the electronic structure and interatomic bonding of the material. In this work, we have combined spectroscopic ellipsometry and VUV spectroscopy to directly determine the optical functions of SiO2 in this range, thereby reducing the uncertainty in the low-energy extrapolation of the data, essential for Kramers-Kronig analysis of VUV reflectance. We report the complex optical properties of SiO2, over the range of 1.5 to 42 eV, showing improved agreement with theory when contrasted with earlier results. In addition to the features previously reported at 10.4, 11.6, 14.03, and 17.10 eV, new interband transitions have been observed at 21.3 eV along with O 2s transitions at 32 eV. We found the bulk plasma peak to be 23.7 eV in the energy loss function spectrum. Based on the magnitude of these new results, the Hamaker constant for SiO2\Vacuum\SiO2 is 71.6 zJ, which is larger than the previously reported value of 66 zJ.