We present temperature-dependent Raman spectra of semimetallic $1{\mathrm{T}\text{−}\mathrm{TiSe}}_{2-\delta }$ single crystals from 10 to 300 K using a 532 nm excitation laser, probing the charge density wave (CDW) transition at 170 K. The first-order $E_g$ and $A_{1g}$ phonon modes exhibit asymmetric lineshapes above 170 K, which are described by the Breit–Wigner–Fano (BWF) function and become Lorentzian below 134 K. The Bose–Einstein anharmonic model reveals anomalies in the $E_g$ phonon peak position near the CDW transition, whereas the $A_{1g}$ mode follows conventional anharmonic behavior. Moreover, we observe six low-frequency Raman peaks between 84 and $123{\mathrm{cm}}^{-1}$, as well as one Raman peak at $295{\mathrm{cm}}^{-1}$. By comparing these features with the one-phonon and two-phonon density of states obtained from the first-principles calculations, we assign the low-frequency modes to defect-induced double-resonance Raman peaks and the $295{\mathrm{cm}}^{-1}$ mode to a two-phonon double-resonance Raman peak. The first-principles calculations also indicate phonon softening near the M and L points in the Brillouin zone, suggesting the lattice instability associated with the CDW transition. Our results provide Raman fingerprints of the CDW transition and highlight the role of electron–phonon interactions in semimetallic $1{\mathrm{T}\text{−}\mathrm{TiSe}}_{2-\delta }$.

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• Electronic structure
• Phase transitions
• Phonons
• First-principles calculations