Thermal coefficients of the wavenumber variation vs. temperature of the peaks P₂ and P₂₉.

Peak	Temperature range	Thermal coefficient, γ (K−1)
P2	T < T1	γ = −1.83 × 10−4
	T 1 < T < T2	γ = 1.23 × 10−3
	T > T2	γ = 6.83 × 10−4
P29	T < T1	γ = −2.48 × 10−5
	T 1 < T < T2	γ = 2.49 × 10−4
	T > T2	γ = 5.97 × 10−5