In a standing wave, the distance between two adjacent nodes or antinodes is half of the wavelength. The first harmonic is the fundamental mode, which has the longest wavelength. For a string of length L, the wavelength of the first harmonic is given by:

$$\lambda_1 = 2L$$

Substituting L = 2.3 meters, we get:

$$\lambda_1 = 2(2.3 \text{ m}) = 4.6 \text{ m}$$

Therefore, the wavelength of the first harmonic is 4.6 meters.